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  • Creating a short unique string for each unique long string

    - by king.net
    I'm trying to create a url shortener system in c# and asp.net mvc. I know about hashtable and I know how to create a redirect system etc. The problem is indexing long urls in database. Some urls may have up to 4000 character length, and it seems it is a bad idea to index this kind of strings. The question is: How can I create a unique short string for each url? for example MD5 can help me? Is MD5 really unique for each string? NOTE: I see that Gravatar uses MD5 for emails, so if each email address is unique, then its MD5 hashed value is unique. Is it right? Can I use same solution for urls?

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  • mysql unique-constraint

    - by Cypher
    I have two tables -- Variables (id, name) and Variable_Entries (id, var_id, value). I want each variable to have a unique set of entries. If I make the value entry unique then a different variable won't be able to have that same value which is not right. Is there some way to make the value column unique for identical var_id's?

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  • Filtering out unique rows in MySQL

    - by jpatokal
    So I've got a large amount of SQL data that looks basically like this: user | src | dst 1 | 1 | 1 1 | 1 | 1 1 | 1 | 2 1 | 1 | 2 2 | 1 | 1 2 | 1 | 3 I want to filter out pairs of (src,dst) that are unique to one user (even if that user has duplicates), leaving behind only those pairs belonging to more than one user: user | src | dst 1 | 1 | 1 1 | 1 | 1 2 | 1 | 1 In other words, pair (1,2) is unique to user 1 and pair (1,3) to user 2, so they're dropped, leaving behind only all instances of pair (1,1). Any ideas? The answers to the question below can find the non-unique pairs, but my SQL-fu doesn't suffice to handle the complication of requiring that they belong to multiple users as well. [SQL question] How to select non "unique" rows

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  • MS SQL Bridge Table Constraints

    - by greg
    Greetings - I have a table of Articles and a table of Categories. An Article can be used in many Categories, so I have created a table of ArticleCategories like this: BridgeID int (PK) ArticleID int CategoryID int Now, I want to create constraints/relationships such that the ArticleID-CategoryID combinations are unique AND that the IDs must exist in the respective primary key tables (Articles and Categories). I have tried using both VS2008 Server Explorer and Enterprise Manager (SQL-2005) to create the FK relationships, but the results always prevent Duplicate ArticleIDs in the bridge table, even though the CategoryID is different. I am pretty sure I am doing something obviously wrong, but I appear to have a mental block at this point. Can anyone tell me please how should this be done? Greaty appreciated!

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  • ASP.NET JavaScript Routing for ASP.NET MVC–Constraints

    - by zowens
    If you haven’t had a look at my previous post about ASP.NET routing, go ahead and check it out before you read this post: http://weblogs.asp.net/zowens/archive/2010/12/20/asp-net-mvc-javascript-routing.aspx And the code is here: https://github.com/zowens/ASP.NET-MVC-JavaScript-Routing   Anyways, this post is about routing constraints. A routing constraint is essentially a way for the routing engine to filter out route patterns based on the day from the URL. For example, if I have a route where all the parameters are required, I could use a constraint on the required parameters to say that the parameter is non-empty. Here’s what the constraint would look like: Notice that this is a class that inherits from IRouteConstraint, which is an interface provided by System.Web.Routing. The match method returns true if the value is a match (and can be further processed by the routing rules) or false if it does not match (and the route will be matched further along the route collection). Because routing constraints are so essential to the route matching process, it was important that they be part of my JavaScript routing engine. But the problem is that we need to somehow represent the constraint in JavaScript. I made a design decision early on that you MUST put this constraint into JavaScript to match a route. I didn’t want to have server interaction for the URL generation, like I’ve seen in so many applications. While this is easy to maintain, it causes maintenance issues in my opinion. So the way constraints work in JavaScript is that the constraint as an object type definition is set on the route manager. When a route is created, a new instance of the constraint is created with the specific parameter. In its current form the constraint function MUST return a function that takes the route data and will return true or false. You will see the NotEmpty constraint in a bit. Another piece to the puzzle is that you can have the JavaScript exist as a string in your application that is pulled in when the routing JavaScript code is generated. There is a simple interface, IJavaScriptAddition, that I have added that will be used to output custom JavaScript. Let’s put it all together. Here is the NotEmpty constraint. There’s a few things at work here. The constraint is called “notEmpty” in JavaScript. When you add the constraint to a parameter in your C# code, the route manager generator will look for the JsConstraint attribute to look for the name of the constraint type name and fallback to the class name. For example, if I didn’t apply the “JsConstraint” attribute, the constraint would be called “NotEmpty”. The JavaScript code essentially adds a function to the “constraintTypeDefs” object on the “notEmpty” property (this is how constraints are added to routes). The function returns another function that will be invoked with routing data. Here’s how you would use the NotEmpty constraint in C# and it will work with the JavaScript routing generator. The only catch to using route constraints currently is that the following is not supported: The constraint will work in C# but is not supported by my JavaScript routing engine. (I take pull requests so if you’d like this… go ahead and implement it).   I just wanted to take this post to explain a little bit about the background on constraints. I am looking at expanding the current functionality, but for now this is a good start. Thanks for all the support with the JavaScript router. Keep the feedback coming!

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  • SQL Constraints &ndash; CHECK and NOCHECK

    - by David Turner
    One performance issue i faced at a recent project was with the way that our constraints were being managed, we were using Subsonic as our ORM, and it has a useful tool for generating your ORM code called SubStage – once configured, you can regenerate your DAL code easily based on your database schema, and it can even be integrated into your build as a pre-build event if you want to do this.  SubStage also offers the useful feature of being able to generate DDL scripts for your entire database, and can script your data for you too. The problem came when we decided to use the generate scripts feature to migrate the database onto a test database instance – it turns out that the DDL scripts that it generates include the WITH NOCHECK option, so when we executed them on the test instance, and performed some testing, we found that performance wasn’t as expected. A constraint can be disabled, enabled but not trusted, or enabled and trusted.  When it is disabled, data can be inserted that violates the constraint because it is not being enforced, this is useful for bulk load scenarios where performance is important.  So what does it mean to say that a constraint is trusted or not trusted?  Well this refers to the SQL Server Query Optimizer, and whether it trusts that the constraint is valid.  If it trusts the constraint then it doesn’t check it is valid when executing a query, so the query can be executed much faster. Here is an example base in this article on TechNet, here we create two tables with a Foreign Key constraint between them, and add a single row to each.  We then query the tables: 1 DROP TABLE t2 2 DROP TABLE t1 3 GO 4 5 CREATE TABLE t1(col1 int NOT NULL PRIMARY KEY) 6 CREATE TABLE t2(col1 int NOT NULL) 7 8 ALTER TABLE t2 WITH CHECK ADD CONSTRAINT fk_t2_t1 FOREIGN KEY(col1) 9 REFERENCES t1(col1) 10 11 INSERT INTO t1 VALUES(1) 12 INSERT INTO t2 VALUES(1) 13 GO14 15 SELECT COUNT(*) FROM t2 16 WHERE EXISTS17 (SELECT *18 FROM t1 19 WHERE t1.col1 = t2.col1) This all works fine, and in this scenario the constraint is enabled and trusted.  We can verify this by executing the following SQL to query the ‘is_disabled’ and ‘is_not_trusted’ properties: 1 select name, is_disabled, is_not_trusted from sys.foreign_keys This gives the following result: We can disable the constraint using this SQL: 1 alter table t2 NOCHECK CONSTRAINT fk_t2_t1 And when we query the constraints again, we see that the constraint is disabled and not trusted: So the constraint won’t be enforced and we can insert data into the table t2 that doesn’t match the data in t1, but we don’t want to do this, so we can enable the constraint again using this SQL: 1 alter table t2 CHECK CONSTRAINT fk_t2_t1 But when we query the constraints again, we see that the constraint is enabled, but it is still not trusted: This means that the optimizer will check the constraint each time a query is executed over it, which will impact the performance of the query, and this is definitely not what we want, so we need to make the constraint trusted by the optimizer again.  First we should check that our constraints haven’t been violated, which we can do by running DBCC: 1 DBCC CHECKCONSTRAINTS (t2) Hopefully you see the following message indicating that DBCC completed without finding any violations of your constraint: Having verified that the constraint was not violated while it was disabled, we can simply execute the following SQL:   1 alter table t2 WITH CHECK CHECK CONSTRAINT fk_t2_t1 At first glance this looks like it must be a typo to have the keyword CHECK repeated twice in succession, but it is the correct syntax and when we query the constraints properties, we find that it is now trusted again: To fix our specific problem, we created a script that checked all constraints on our tables, using the following syntax: 1 ALTER TABLE t2 WITH CHECK CHECK CONSTRAINT ALL

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  • Using Constraints on Hierarchical Data in a Self-Referential Table

    - by pbarney
    Suppose you have the following table, intended to represent hierarchical data: +--------+-------------+ | Field | Type | +--------+-------------+ | id | int(10) | | parent | int(10) | | name | varchar(45) | +--------+-------------+ The table is self-referential in that the parent_id refers to id. So you might have the following data: +----+--------+---------------+ | id | parent | name | +----+--------+---------------+ | 1 | 0 | fruit | | 2 | 0 | vegetable | | 3 | 1 | apple | | 4 | 1 | orange | | 5 | 3 | red delicious | | 6 | 3 | granny smith | | 7 | 3 | gala | +----+--------+---------------+ Using MySQL, I am trying to impose a (self-referential) foreign key constraint upon the data to update on cascades and prevent deletion of fruit if they have "children." So I used the following: CREATE TABLE `idtlp_main`.`fruit` ( `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `parent` INT(10) UNSIGNED, `name` VARCHAR(45) NOT NULL, PRIMARY KEY (`id`), CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT ) ENGINE = InnoDB; From what I understand, this should fit my requirements. (And parent must default to null to allow insertions, correct?) The problem is, if I change the id of a record, it will not cascade: Cannot delete or update a parent row: a foreign key constraint fails (`iddoc_main`.`fruit`, CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE) What am I missing? Feel free to correct me if my terminology is screwed up... I'm new to constraints.

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  • Primary Key Identity Value Increments On Unique Key Constraint Violation

    - by Jed
    I have a SqlServer 2008 table which has a Primary Key (IsIdentity=Yes) and three other fields that make up a Unique Key constraint. In addition I have a store procedure that inserts a record into the table and I call the sproc via C# using a SqlConnection object. The C# sproc call works fine, however I have noticed interesting results when the C# sproc call violates the Unique Key constraint.... When the sproc call violates the Unique Key constraint, a SqlException is thrown - which is no surprise and cool. However, I notice that the next record that is successfully added to the table has a PK value that is not exactly one more than the previous record - For example: Say the table has five records where the PK values are 1,2,3,4, and 5. The sproc attempts to insert a sixth record, but the Unique Key constraint is violated and, so, the sixth record is not inserted. Then the sproc attempts to insert another record and this time it is successful. - This new record is given a PK value of 7 instead of 6. Is this normal behavior? If so, can you give me a reason why this is so? (If a record fails to insert, why is the PK index incremented?) If this is not normal behavior, can you give me any hints as to why I am seeing these symptoms?

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  • Unique SMS sender id?

    - by Pascal
    Hello, I want to build an app that send SMS to people. However, I want my users to know that the SMS comes from the app and nothing else so they can't fake it. Is there a way to guarantee that the sender ID is unique to my app? It seems that sending a SMS by phone is with a unique SENDER ID for each phone number. But, from what I read, I don't think it is the case when sending a SMS through a web gateway. Is this correct? I am not an expert in mobile phone security. Of course, I am willing to pay the price for a unique sender id, if such thing is possible. Regards, Pascal

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  • R - find and calculate with unique combinations of values

    - by lecodesportif
    I would like to work with unique combinations of var1 and var2. foo <- data.frame(var1= c(1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4), var2=c(1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 2, 2, 3, 3)) As has been noted (+1 for answers), unique(foo) results in this: var1 var2 1 1 1 2 2 1 3 2 2 4 3 1 5 3 2 6 4 2 7 4 3 Based on the unique combinations, how do I get the number of occurrences of a var1 value and the sum (bla) of each var1 value's var2 values. The output could look like this: var1 n bla 1 1 1 1 2 2 2 3 3 3 2 3 4 4 2 5 edit: The question was too basic and probably duplicate so I extended it.

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  • SharePoint: Unique column values

    - by Anoop
    I Want to have only unique values in a SharePoin List. To achieve this I can use 'ItemAdding' event handler as mentioned in the below link. http://weblogs.asp.net/vikram/archive/2008/12/24/sharepoint-using-event-handler-to-make-a-column-unique.aspx Now I have a Doubt: Suppose that two user tries to add list Item in the list with the same column value(which requires unique value) at the same Time. will ItemAdding event would be fired at the same time for both call? If so then there is a possibility that two items having same value in the column. Please confirm.

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  • How to generate unique number of 12 digits?

    - by DanSogaard
    I'm working on an app that sends raw data to zebra printer and print out barcodes. And since every item has its own unique barcode, I need to define a variable that automatically generates unique number of 12 digits long. see example: printBar prnt = new printBar("123456789012"); Is there anyway to define a double variable and pass it to a function that return uniqely 12 digits number and pass it over again to the printBar class?. But how to make sure everytime you access it returns a unique value?. I also thought of another way, since am using MS Access db, I can create a column of AutoNumber datatype and assign it to Random, but you don't get the exact 12 digits required, sometimes it generates a value of 10 digits sometimes more or less.

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  • Enforcing Constraints Upon Data Documents of Various Formats

    - by Christopher Berman
    This seems like the sort of problem that must have been solved elegantly long ago, but I haven't the foggiest how to google it and find it. Suppose you're maintaining a large legacy system, which has a large collection of data (tens of GB) of various formats, including XML and two different internal configuration formats. Suppose further that there are abstract rules governing the values these files may or may not contain. EXAMPLE: File A defines the raw, mathematical data pertaining to the aerodynamics of a car for consumption of the physics component of the system. File B contains certain values from File A in an easily accessible, XML hierarchy for consumption of a different component of the system. There exists, therefore, an abstract rule (or constraint) such that the values from File B must match the values from File A. This is probably the simplest constraint that can be specified, but in practice, the constraints between files can become very complicated indeed. What is the best method for managing these constraints between files of arbitrary formats, short of migrating it over to an RDBMS (which simply isn't feasible for the foreseeable future)? Has this problem been solved already? To be more specific, I would expect the solution to at least produce notifications of violated constraints; the solution need not resolve the constraints. ============================== Sample file structures File A (JeepWrangler2011.emv): MODEL JeepWrangler2011 { EsotericMathValueX 11.1 EsotericMathValueY 22.2 EsotericMathValueZ 33.3 } File B (JeepWrangler2011.xml): <model name="JeepWrangler2011"> <!--These values must correspond File A's EsotericMathValues--> <modelExtent x="11.1" y="22.2" z="33.3"/> [...] </model>

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  • mysql create table help with unique

    - by Matt
    I'm trying to create a table, and can't figure out how to assign two columns to be unique.. I know how to alter a table thats already created, but how do you do it in the create.. im after a create if not exist col1 TEXT, col2 TEXT, col3 TEXT unique(col1, col2) ^very rough basic but you get the idea

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  • SQL Server: "Mostly-unique" index

    - by Ian Boyd
    In a table i want to ensure that only unique vales exist over the five-column key: Timestamp Account RatingDate TripHistoryKey EventAction ========= ======= ========== ============== =========== 2010511 1234 2010511 1 INSERT 2010511 1234 2010511 4 INSERT 2010511 1234 2010511 7 INSERT 2010511 1234 2010511 1 INSERT <---duplicate But i only want the unique constraint to apply between rows when EventAction is INSERT: Timestamp Account RatingDate TripHistoryKey EventAction ========= ======= ========== ============== =========== 2010511 1234 2010511 1 INSERT 2010511 1234 2010511 1 UPDATE 2010511 1234 2010511 1 UPDATE <---not duplicate 2010511 1234 2010511 1 UPDATE <---not duplicate 2010511 1234 2010511 1 DELETE <---not duplicate 2010511 1234 2010511 1 DELETE <---not duplicate 2010511 1234 2010511 1 INSERT <---DUPLICATE Possible?

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  • Determining if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • Determing if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • In VB.NET how do you specify Inherits/implements on a generic class with multi-constraints

    - by Romel Evans
    When I write the following statement in VB.Net (C# is my normal language), I get an "end of statement expected" referring to the "Implements" statement. <Serializable()> _ <XmlSchemaProvider("EtgSchema")> _ Public Class SerializeableEntity(Of T As {Class, ISerializable, New}) _ Implements IXmlSerializable, ISerializable ... End Class The C# version that I'm trying to emulate is: [Serializable] [XmlSchemaProvider("MySchema")] public class SerializableEntity<T> : IXmlSerializable, ISerializable where T : class, new() { .... } Sometimes I feel like I have 5 thumbs with VB.NET :)

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  • PostgreSQL - disabling constraints

    - by azp74
    I have a table with approx 5 million rows which has a fk constraint referencing the primary key of another table (also approx 5 million rows). I need to delete about 75000 rows from both tables. I know that if I try doing this with the fk constraint enabled it's going to take an unacceptable amount of time. Coming from an Oracle background my first thought was to disable the constraint, do the delete & then reenable the constraint. PostGres appears to let me disable constraint triggers if I am a super user (I'm not, but I am logging in as the user that owns/created the objects) but that doesn't seem to be quite what I want. The other option is to drop the constraint and then reinstate it. I'm worried that rebuilding the constraint is going to take ages given the size of my tables. Any thoughts?

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  • Generic Type Parameter constraints in C# .NET

    - by activwerx
    Consider the following Generic class: public class Custom<T> where T : string { } This produces the following error: 'string' is not a valid constraint. A type used as a constraint must be an interface, a non-sealed class or a type parameter. Is there another way to constrain which types my generic class can use? Also, can I constrain to multiple types? E.G. T can only be string, int or byte

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  • integrity Constraints on a table.

    - by Dinesh
    See this sample schema Passenger(id PK, Name) Plane(id PK, capacity, type); Flight(id PK, planeId FK(Plane), flightDate, StartLocation, destination) CREATE TABLE Reservation(PassengerId, flightId, PRIMARY KEY (passengerId, flightId), FOREIGN KEY (passengerId) REFERENCES Passenger, FOREIGN KEY (flightId) REFERENCES Flight); I need to define an integrity constraint that enforces the restriction that the number of passengers on a plane cannot exceed the plane’s capacity. I have tried and achieved so far is this. CREATE TABLE Reservation( passengerId INTEGER, flightId INTEGER, PRIMARY KEY (passengerId, flightId), FOREIGN KEY (passengerId) REFERENCES Passenger, FOREIGN KEY (flightId) REFERENCES Flight, Constraint check1 check(Not Exists(select * from Flight s, (select count(*) as totalRes from Reservation group by flightId) t where t.totalRes > s.capacity ) ) ); I am not sure i am doing in right way or not. Any suggestions?

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  • how can i set up a uniqueness constraint in mysql for columns that can be null?

    - by user299689
    I know that in MySQL, UNIQUE constraits don't treat NULL values as equal. So if I have a unique constraint on ColumnX, then two separate rows can have values of NULL for ColumnX and this wouldn't violate the constraint. How can I work around this? I can't just set the value to an arbitrary constant that I can flag, because ColumnX in my case is actually a foreign key to another table. What are my options here? Please note that this table also has an "id" column that is its primary key. Since I'm using Ruby on Rails, it's important to keep this id column as the primary key. Note 2: In reality, my unique key encompasses many columns, and some of them have to be null, because they are foreign keys, and only one of them should be non-null. What I'm actually trying to do is to "simulate" a polymorphic relationship in a way that keep referential integrity in the db, but using the technique outlined in the first part of the question asked here: http://stackoverflow.com/questions/922184/why-can-you-not-have-a-foreign-key-in-a-polymorphic-association

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