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  • Django many to many queries

    - by Hulk
    In the following, How to get designation when querying Emp sc=Emp.objects.filter(pk=profile.emp.id)[0] sc.desg //this gives an error class Emp(models.Model): name = models.CharField(max_length=255, unique=True) address1 = models.CharField(max_length=255) city = models.CharField(max_length=48) state = models.CharField(max_length=48) country = models.CharField(max_length=48) desg = models.ManyToManyField(Designation) class Designation(models.Model): description = models.TextField() title = models.TextField() def __unicode__(self): return self.board

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  • Help writing database queries for derby?

    - by outsyncof
    I have a database containing multiple tables (Person, Parents, etc) Person table has certain attributes particularly ssn, countryofbirth and currentcountry. Parents table has ssn, and fathersbirthcountry I'm trying to output the SSNs of all people who have the same countryofbirth as their fathersbirthcountry and also have same currentcountry as fathersbirthcountry. SELECT Person.ssn FROM Person, Parents WHERE fathersbirthcountry = countryofbirth AND currentcountry = fathersbirthcountry; the above doesn't seem to be working, could anyone please help me out?

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  • Django queries Especial Caracters

    - by Jorge Machado
    Hi, I Working on location from google maps and using django to. My question is: I have a String in request.GET['descricao'] lets say it contains "Via rapida". In my database i have store = "Via Rápida" i'm doing : local = Local.objects.filter(name__icontains=request.GET['descricao']) with that i can get everthing fine like "Via Rapida" but the result that have "Via rápida" never get match in the query (ASCI caracter may be ?) what must i do given a string "Via rapida" match "via rápida" and "via rapida" ? Regular Expressions ? how ? Thanks

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  • JUnit Parameterized Runner and mvn Surefire Report integration

    - by fraido
    I'm using the Junit Parameterized Runner and the Maven Plugin Surefire Report to generate detailed reports during the mvn site phase. I've something like this @RunWith(Parameterized.class) public class MyTest { private String string1; private String string2; @Parameterized.Parameters public static Collection params() { return Arrays.asList(new String[][] { { "1", "2"}, { "3", "4"}, { "5", "6"} }); } public MyTest(String string1, String string2) { this.string1 = string1; this.string2 = string2; } @Test public void myTestMethod() { ... } @Test public void myOtherTestMethod() { ... } The report shows something like myTestMethod[0] 0.018 myTestMethod[1] 0.009 myTestMethod[2] 0.009 ... myOtherTestMethod[0] 0.018 myOtherTestMethod[1] 0.009 myOtherTestMethod[2] 0.009 ... Is there a way to display something else rather than the iteration number [0]..[1]..etc.. The constructor parameters would be a much better information. For example myTestMethod["1", "2"] 0.018 ...

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  • SQL SERVER – Identify Most Resource Intensive Queries – SQL in Sixty Seconds #028 – Video

    - by pinaldave
    During performance tuning conversation the very first question people often ask is what are the queries offending the server or in another word let us identify the queries which are the most resource intensive. The resources are often described as either Memory, CPU or IO. When we talk about the queries the same is applicable for them as well. The query which is doing lots of reads or writes are for sure resource intensive as well query which are taking maximum CPU time. Performance tuning is a very deep subject and we all have our own preference regarding what should be the first step to tuning and what should be looked with the salt of grain. Though there is no denying that a query which uses more resources than what it should be using for sure require tuning. There are many ways to do identify query using intense resources (e.g. Extended events etc) but in this one we will go by simple DMV. There is a small gotcha we all have to remember about usage of DMV is that it only brings back results from existing cache. So if you have a query which is very resource intensive but is not cached or if you have explicitly removed the query from the cache it will be not part of the result returned by this DMV. It is quite possible that a query is aged and removed from the cache if your cache is not huge. If your cache is large you may want to be careful in running this query during business hours as this query itself can be resource intensive. Get Script to identify resource intensive query from Here Related Tips in SQL in Sixty Seconds: SQL SERVER – Find Most Expensive Queries Using DMV Simple Example to Configure Resource Governor – Introduction to Resource Governor SQL SERVER – DMV – sys.dm_exec_query_optimizer_info – Statistics of Optimizer SQL SERVER – Wait Stats – Wait Types – Wait Queues – Day 0 of 28 Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Excel

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  • C# - How to store and reuse queries

    - by Jason Holland
    I'm learning C# by programming a real monstrosity of an application for personal use. Part of my application uses several SPARQL queries like so: const string ArtistByRdfsLabel = @" PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT DISTINCT ?artist WHERE {{ {{ ?artist rdf:type <http://dbpedia.org/ontology/MusicalArtist> . ?artist rdfs:label ?rdfsLabel . }} UNION {{ ?artist rdf:type <http://dbpedia.org/ontology/Band> . ?artist rdfs:label ?rdfsLabel . }} FILTER ( str(?rdfsLabel) = '{0}' ) }}"; string Query = String.Format(ArtistByRdfsLabel, Artist); I don't like the idea of keeping all these queries in the same class that I'm using them in so I thought I would just move them into their own dedicated class to remove clutter in my RestClient class. I'm used to working with SQL Server and just wrapping every query in a stored procedure but since this is not SQL Server I'm scratching my head on what would be the best for these SPARQL queries. Are there any better approaches to storing these queries using any special C# language features (or general, non C# specific, approaches) that I may not already know about?

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  • Using Queries with Coherence Read-Through Caches

    - by jpurdy
    Applications that rely on partial caches of databases, and use read-through to maintain those caches, have some trade-offs if queries are required. Coherence does not support push-down queries, so queries will apply only to data that currently exists in the cache. This is technically consistent with "read committed" semantics, but the potential absence of data may make the results so unintuitive as to be useless for most use cases (depending on how much of the database is held in cache). Alternatively, the application itself may manually "push down" queries to the database, either retrieving results equivalent to querying the cache directly, or may query the database for a key set and read the values from the cache (relying on read-through to handle any missing values). Obviously, if the result set is too large, reading through the cache may cause significant thrashing. It's also worth pointing out that if the cache is asynchronously synchronized with the database (perhaps via database change listener), that an application may commit a transaction to the database, then generate a key set from the database via a query, then read cache entries through the cache, possibly resulting in a race condition where the application sees older data than it had previously committed. In theory this is not problematic but in practice it is very unintuitive. For this reason it often makes sense to invalidate the cache when updating the database, forcing the next read-through to update the cache.

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  • Joins in single-table queries

    - by Rob Farley
    Tables are only metadata. They don’t store data. I’ve written something about this before, but I want to take a viewpoint of this idea around the topic of joins, especially since it’s the topic for T-SQL Tuesday this month. Hosted this time by Sebastian Meine (@sqlity), who has a whole series on joins this month. Good for him – it’s a great topic. In that last post I discussed the fact that we write queries against tables, but that the engine turns it into a plan against indexes. My point wasn’t simply that a table is actually just a Clustered Index (or heap, which I consider just a special type of index), but that data access always happens against indexes – never tables – and we should be thinking about the indexes (specifically the non-clustered ones) when we write our queries. I described the scenario of looking up phone numbers, and how it never really occurs to us that there is a master list of phone numbers, because we think in terms of the useful non-clustered indexes that the phone companies provide us, but anyway – that’s not the point of this post. So a table is metadata. It stores information about the names of columns and their data types. Nullability, default values, constraints, triggers – these are all things that define the table, but the data isn’t stored in the table. The data that a table describes is stored in a heap or clustered index, but it goes further than this. All the useful data is going to live in non-clustered indexes. Remember this. It’s important. Stop thinking about tables, and start thinking about indexes. So let’s think about tables as indexes. This applies even in a world created by someone else, who doesn’t have the best indexes in mind for you. I’m sure you don’t need me to explain Covering Index bit – the fact that if you don’t have sufficient columns “included” in your index, your query plan will either have to do a Lookup, or else it’ll give up using your index and use one that does have everything it needs (even if that means scanning it). If you haven’t seen that before, drop me a line and I’ll run through it with you. Or go and read a post I did a long while ago about the maths involved in that decision. So – what I’m going to tell you is that a Lookup is a join. When I run SELECT CustomerID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 285; against the AdventureWorks2012 get the following plan: I’m sure you can see the join. Don’t look in the query, it’s not there. But you should be able to see the join in the plan. It’s an Inner Join, implemented by a Nested Loop. It’s pulling data in from the Index Seek, and joining that to the results of a Key Lookup. It clearly is – the QO wouldn’t call it that if it wasn’t really one. It behaves exactly like any other Nested Loop (Inner Join) operator, pulling rows from one side and putting a request in from the other. You wouldn’t have a problem accepting it as a join if the query were slightly different, such as SELECT sod.OrderQty FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail as sod on sod.SalesOrderID = soh.SalesOrderID WHERE soh.SalesPersonID = 285; Amazingly similar, of course. This one is an explicit join, the first example was just as much a join, even thought you didn’t actually ask for one. You need to consider this when you’re thinking about your queries. But it gets more interesting. Consider this query: SELECT SalesOrderID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 276 AND CustomerID = 29522; It doesn’t look like there’s a join here either, but look at the plan. That’s not some Lookup in action – that’s a proper Merge Join. The Query Optimizer has worked out that it can get the data it needs by looking in two separate indexes and then doing a Merge Join on the data that it gets. Both indexes used are ordered by the column that’s indexed (one on SalesPersonID, one on CustomerID), and then by the CIX key SalesOrderID. Just like when you seek in the phone book to Farley, the Farleys you have are ordered by FirstName, these seek operations return the data ordered by the next field. This order is SalesOrderID, even though you didn’t explicitly put that column in the index definition. The result is two datasets that are ordered by SalesOrderID, making them very mergeable. Another example is the simple query SELECT CustomerID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 276; This one prefers a Hash Match to a standard lookup even! This isn’t just ordinary index intersection, this is something else again! Just like before, we could imagine it better with two whole tables, but we shouldn’t try to distinguish between joining two tables and joining two indexes. The Query Optimizer can see (using basic maths) that it’s worth doing these particular operations using these two less-than-ideal indexes (because of course, the best indexese would be on both columns – a composite such as (SalesPersonID, CustomerID – and it would have the SalesOrderID column as part of it as the CIX key still). You need to think like this too. Not in terms of excusing single-column indexes like the ones in AdventureWorks2012, but in terms of having a picture about how you’d like your queries to run. If you start to think about what data you need, where it’s coming from, and how it’s going to be used, then you will almost certainly write better queries. …and yes, this would include when you’re dealing with regular joins across multiples, not just against joins within single table queries.

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  • Check/Monitor Amount of SQL Queries per Hour

    - by deathlock
    My website is hosted on a shared hosting and I'd like to know how much SQL queries it is using per hour. I tried to navigate through cPanel and I find nothing to check or monitor the amount of SQL queries per hour. I tried to ask my host and they said it is not possible to do manually. However I found this http://forum.powweb.com/archive/index.php/t-49937.html and another one on Stackoverflow: http://stackoverflow.com/questions/9842094/sql-how-can-i-get-the-number-of-executed-queries-per-database-or-hour-or And since this exists, I assume that it is actually possible. Problem is I can't execute that in my phpmyAdmin. Can someone here guide me through the process?

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  • System.Data.SQLite parameterized queries with multiple values?

    - by Rezzie
    I am trying to do run a bulk deletion using parameterized queries. Currently, I have the following code: pendingDeletions = new SQLiteCommand(@"DELETE FROM [centres] WHERE [name] = $name", conn); foreach (string name in selected) pendingDeletions.Parameters.AddWithValue("$name", centre.Name); pendingDeletions.ExecuteNonQuery(); However, the value of the parameter seems to be overwritten each time and I end up just removing the last centre. What is the correct way to execute a parameterized query with a list of values?

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  • How can I handle parameterized queries in Drupal?

    - by Anthony Gatlin
    We have a client who is currently using Lotus Notes/Domino as their content management system and web server. For many reasons, we are recommending they sunset their Notes/Domino implementation and transition onto a more modern platform--such as Drupal. The client has several web applications which would be a natural fit for Drupal. However, I am unsure of the best way to implement one of the web applications in Drupal. I am running into a knowledge barrier and wondered if any of you could fill in the gaps. Situation The client has a Lotus Domino application which serves as a front-end for querying a large DB2 data store and returning a result set (generally in table form) to a user via the web. The web application provides access to approximately 100 pre-defined queries--50 of which are public and 50 of which are secured. Most of the queries accept some set of user selected parameters as input. The output of the queries is typically returned to users in a list (table) format. A limited number of result sets allow drill-down through the HTML table into detail records. The query parameters often involve database queries themselves. For example, a single query may pull a list of company divisions into a drop-down. Once a division is selected, second drop-down with the departments from that division is populated--but perhaps only departments which meet some special criteria--such as those having taken a loss within a specific time frame. Most queries have 2-4 parameters with the average probably being 3. The application involves no data entry. None of the back-end data is ever modified by the web application. All access is purely based around querying data and viewing results. The queries change relatively infrequently, and the current system has been in place for approximately 10 years. There may be 10-20 query additions, modifications, or other changes in a given year. The client simply desires to change the presentation platform but absolutely does not want to re-do the 100 database queries. Once the project is implemented, the client wants their staff to take over and manage future changes. The client's staff have no background in Drupal or PHP but are somewhat willing to learn as necessary. How would you transition this into Drupal? My major knowledge void relates to how we would manage the query parameters and access the queries themselves. Here are a few specific questions but feel free to chime in on any issue related to this implementation. Would we have to build 100 forms by hand--with each form containing the parameters for a given query? If so, how would we do this? Approximately how long would it take to build/configure each of these forms? Is there a better way than manually building 100 forms? (I understand using CCK to enter data into custom content types but since we aren't adding any nodes, I am a little stuck as to how this might work.) Would it be possible for the internal staff to learn to create these query parameter forms--even if they are unfamiliar with Drupal today? Would they be required to do any PHP programming? How would we take the query parameters from a form and execute a query against DB2? Would this require a custom module? If so, would it require one module total or one module per query? (Note: There is apparently a DB2 driver available for Drupal. See http://groups.drupal.org/node/5511.) Note: I am not looking for CMS recommendations other than Drupal as Drupal nicely fits all of the client's other requirements, and I hope to help them standardize on a single platform. Any assistance you can provide would be helpful. Thank you in advance for your help!

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  • MYSQL - Selecting a specific date range to get "current" popular screensavers.

    - by Joe
    Let's say I have a screensaver website. I want to display the CURRENT top 100 screensavers on the front page of the website. What I mean is, "RECENT" top 100 screensavers. What would be an example query to do this? My current one is: SELECT * FROM tbl_screensavers WHERE WEEK(tbl_screensavers.DateAdded) = WEEK('".date("Y-m-d H:i:s",strtotime("-1 week"))."') ORDER BY tbl_screensavers.ViewsCount, tbl_screensavers.DateAdded This will select the most viewed ("tbl_screensavers.ViewsCount") screensavers that were added ("tbl_screensavers.DateAdded") in the last week. However, in some cases there are no screensavers, or less than 100 screensavers, submitted in that week. So, how can I perform a query which would select "RECENT" top 100 screensavers? Hopefully you have an idea of what I'm try to accomplish when I say "RECENT" or "CURRENT" top screensavers. -- aka. the most viewed, recently - not the most viewed, all-time.

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  • LINQ to Twitter Queries with LINQPad

    - by Joe Mayo
    LINQPad is a popular utility for .NET developers who use LINQ a lot.  In addition to standard SQL queries, LINQPad also supports other types of LINQ providers, including LINQ to Twitter.  The following sections explain how to set up LINQPad for making queries with LINQ to Twitter. LINQPad comes in a couple versions and this example uses LINQPad4, which runs on the .NET Framework 4.0. 1. The first thing you'll need to do is set up a reference to the LinqToTwitter.dll. From the Query menu, select query properties. Click the Browse button and find the LinqToTwitter.dll binary. You should see something similar to the Query Properties window below. 2. While you have the query properties window open, add the namespace for the LINQ to Twitter types.  Click the Additional Namespace Imports tab and type in LinqToTwitter. The results are shown below: 3. The default query type, when you first start LINQPad, is C# Expression, but you'll need to change this to support multiple statements.  Change the Language dropdown, on the Main window, to C# Statements. 4. To query LINQ to Twitter, instantiate a TwitterContext, by typing the following into the LINQPad Query window: var ctx = new TwitterContext(); Note: If you're getting syntax errors, go back and make sure you did steps #2 and #3 properly. 5. Next, add a query, but don't materialize it, like this: var tweets = from tweet in ctx.Status where tweet.Type == StatusType.Public select new { tweet.Text, tweet.Geo, tweet.User }; 6. Next, you want the output to be displayed in the LINQPad grid, so do a Dump, like this: tweets.Dump(); The following image shows the final results:   That was an unauthenticated query, but you can also perform authenticated queries with LINQ to Twitter's support of OAuth.  Here's an example that uses the PinAuthorizer (type this into the LINQPad Query window): var auth = new PinAuthorizer { Credentials = new InMemoryCredentials { ConsumerKey = "", ConsumerSecret = "" }, UseCompression = true, GoToTwitterAuthorization = pageLink => Process.Start(pageLink), GetPin = () => { // this executes after user authorizes, which begins with the call to auth.Authorize() below. Console.WriteLine("\nAfter you authorize this application, Twitter will give you a 7-digit PIN Number.\n"); Console.Write("Enter the PIN number here: "); return Console.ReadLine(); } }; // start the authorization process (launches Twitter authorization page). auth.Authorize(); var ctx = new TwitterContext(auth, "https://api.twitter.com/1/", "https://search.twitter.com/"); var tweets = from tweet in ctx.Status where tweet.Type == StatusType.Public select new { tweet.Text, tweet.Geo, tweet.User }; tweets.Dump(); This code is very similar to what you'll find in the LINQ to Twitter downloadable source code solution, in the LinqToTwitterDemo project.  For obvious reasons, I changed the value assigned to ConsumerKey and ConsumerSecret, which you'll have to obtain by visiting http://dev.twitter.com and registering your application. One tip, you'll probably want to make this easier on yourself by creating your own DLL that encapsulates all of the OAuth logic and then call a method or property on you custom class that returns a fully functioning TwitterContext.  This will help avoid adding all this code every time you want to make a query. Now, you know how to set up LINQPad for LINQ to Twitter, perform unauthenticated queries, and perform queries with OAuth. Joe

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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  • Precompiling LINQ Queries

    Did you know that by precompiling LINQ queries you might actually be degrading your app’s performance if you’re not careful? Julie Lerman explains how to ensure you’re not re-precompiling queries each time and losing the expected performance benefits across post-backs, short-lived service operations and other code where critical instances are going out of scope.

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  • Should experienced programmers know database queries?

    - by Shamim Hafiz
    There are so many programmers out there who are also an expert at Query writing and Database design. Should this be a core requirement to be an expert programmer or software engineer? Though there are lots of similarities in the way queries and codes are developed, my personal opinion is, Queries seem to have a different Structure than Code and it can be tough to Master both simultaneously due to the different approaches.

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  • phpMyAdmin - Display all queries

    - by Carlos Fernández San Millán
    I have installed a fresh desktop with ubuntu quantal and the following packages versions: MySQL: 5.5.28-0ubuntu0.12.10.1 Apache: 2.2.22 (Ubuntu) phpMyAdmin: 3.4.11.1deb1 I would like phpmyadmin to display all the queries I run. How can I do it? Thank you very much. UPDATE To be more specific, there are some queries showing into the query box, but I would like phpMyAdmin to show ALL of them including when I export a Database (if possible). Thank you.

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  • Interpreting Munin graphs showing available entropy and MySQL slow queries in sync

    - by user64204
    We're experiencing performance issues on our website, and after reviewing our munin graphs, the only metrics we've found in sync are Available entropy and MySQL slow queries, with the latter influenced by our number of logged in users: Based on the wikipedia entropy page, my understanding is that entropy is the amount of randomness (here measured in bytes) that the system can use for various tasks, mainly cryptography and functions that require random input. Since the peaks in available entropy and MySQL slow queries are occurring in sync and at regular interval, that the number of MySQL slow queries is proportional to our number of Drupal users whereas the peaks in available entropy seem to be much more constant and less proportional to these 2 metrics, we're thinking available entropy is the reflect of a root cause which, combined with the traffic to our website, is causing those slow queries (and not the opposite, slow queries influencing the entropy). Accordingly: Q: What underlying problem do you think could cause regular peaks in available entropy that could have an influence on MySQL's ability to process queries?

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  • Advanced Record-Level Business Intelligence with Inner Queries

    - by gt0084e1
    While business intelligence is generally applied at an aggregate level to large data sets, it's often useful to provide a more streamlined insight into an individual records or to be able to sort and rank them. For instance, a salesperson looking at a specific customer could benefit from basic stats on that account. A marketer trying to define an ideal customer could pull the top entries and look for insights or patterns. Inner queries let you do sophisticated analysis without the overhead of traditional BI or OLAP technologies like Analysis Services. Example - Order History Constancy Let's assume that management has realized that the best thing for our business is to have customers ordering every month. We'll need to identify and rank customers based on how consistently they buy and when their last purchase was so sales & marketing can respond accordingly. Our current application may not be able to provide this and adding an OLAP server like SSAS may be overkill for our needs. Luckily, SQL Server provides the ability to do relatively sophisticated analytics via inner queries. Here's the kind of output we'd like to see. Creating the Queries Before you create a view, you need to create the SQL query that does the calculations. Here we are calculating the total number of orders as well as the number of months since the last order. These fields might be very useful to sort by but may not be available in the app. This approach provides a very streamlined and high performance method of delivering actionable information without radically changing the application. It's also works very well with self-service reporting tools like Izenda. SELECT CustomerID,CompanyName, ( SELECT COUNT(OrderID) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID ) As Orders, DATEDIFF(mm, ( SELECT Max(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) ,getdate() ) AS MonthsSinceLastOrder FROM Customers Creating Views To turn this or any query into a view, just put CREATE VIEW AS before it. If you want to change it use the statement ALTER VIEW AS. Creating Computed Columns If you'd prefer not to create a view, inner queries can also be applied by using computed columns. Place you SQL in the (Formula) field of the Computed Column Specification or check out this article here. Advanced Scoring and Ranking One of the best uses for this approach is to score leads based on multiple fields. For instance, you may be in a business where customers that don't order every month require more persistent follow up. You could devise a simple formula that shows the continuity of an account. If they ordered every month since their first order, they would be at 100 indicating that they have been ordering 100% of the time. Here's the query that would calculate that. It uses a few SQL tricks to make this happen. We are extracting the count of unique months and then dividing by the months since initial order. This query will give you the following information which can be used to help sales and marketing now where to focus. You could sort by this percentage to know where to start calling or to find patterns describing your best customers. Number of orders First Order Date Last Order Date Percentage of months order was placed since last order. SELECT CustomerID, (SELECT COUNT(OrderID) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) As Orders, (SELECT Max(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) AS LastOrder, (SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) AS FirstOrder, DATEDIFF(mm,(SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID),getdate()) AS MonthsSinceFirstOrder, 100*(SELECT COUNT(DISTINCT 100*DATEPART(yy,OrderDate) + DATEPART(mm,OrderDate)) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) / DATEDIFF(mm,(SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID),getdate()) As OrderPercent FROM Customers

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  • odd behavior with java collections of parameterized Class objects

    - by Paul
    Ran into some questionable behavior using lists of parameterized Class objects: ArrayList<Class<String>> classList = new ArrayList<Class<String>>(); classList.add(Integer.class); //compile error Class intClass = Integer.class; classList.add(intClass); //legal apparently, as long as intClass is not parameterized Found the same behavior for LinkedList, haven't tried other collections. Is it like this for a reason? Or have I stumbled on something?

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  • Google I/O 2010 - Next gen queries

    Google I/O 2010 - Next gen queries Google I/O 2010 - Next gen queries App Engine 301 Alfred Fuller This session will discuss the design and implications of improvements to the Datastore query engine including support for AND, OR and NOT query operators, the solution to exploding indexes and paging backwards with Cursors. Specific technologies discussed will be an improved zigzag merge join algorithm, a new extensible multiquery framework (with geo-query support) and a smaller more versatile Cursor design. For all I/O 2010 sessions, please go to code.google.com From: GoogleDevelopers Views: 16 1 ratings Time: 50:17 More in Science & Technology

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  • Combining Multiple Queries and Parameters into One Operation

    - by shay.shmeltzer
    This question came up twice this week and while the solution is explained in a couple of previous blog entries I did, I thought that showing off the complete solution in a single video would be nice. The scenario is that you have two VOs with queries that are based on a parameter, I showed in the past how to create a parameter form that executes the query - and you can do this for both. But what if you actually need just one value to drive both queries? How do you combine two parameter forms and two buttons into one? This is what this video shows you. The steps are: Creating two parameter forms Setting the value of a parameter in the binding tab Creating a backing bean to execute the code for one button Adding the code to execute another operation Remarking the parts that can be dropped from the screen Check it out here:

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