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• Is an IQueryable a query or just an object which can be queried?

  - by Albic

  I'm kinda confused what the IQueryable interface actually represents. The MSDN documentation for IQueryable says: "Provides functionality to evaluate queries against a specific data source." The documentation for IQueryProvider says: "Defines methods to create and execute queries that are described by an IQueryable object." The name and the documentation summary suggest that it is an object/data store which can be queried. The second quote and the fact the ObjectQuery class from the Entity Framework implements IQueryable suggest it is a query which can be executed. Did I misunderstood something or is it really kinda fuzzy?

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• add Constraint on database with trigger

  - by Am1rr3zA

  Hi, I have 3 tables (Student, Course, student_course_choose(have field grade)) I defined a view on these 3 tables that get me an Average of the each student. I want to have constraint(with trigger) on these view(or on the table that need it) to limit the average of each student between 13 and 18. I somewhere read that I must use foreach statement(instead of foreach row) on trigger because when I decrease some grade of special student and his/her average become less than 13 they don't give me error (because later I increase grade of another his/her course ). how must I wrote this Trigger? (I want to implement aprh for testing trigger) note:I can write it in SQL server, oracle or Mysql no diff for me.

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• Updating multiple tables with LinqToSql in one unit of work

  - by zsharp

  Table 1: int ID-a(pk) Table 2: int ID-a(pk), int ID-b(pk) Table 3: int ID-b(pk), string C I have the data to insert into Table 1. But I do not have the ID-a, which is autogenerated. I have many string C to insert in Table 3. I am trying to insert row into Table 1, get the ID-a to insert in Table 2 along with the ID-b that is auto-Generated in Table 3 when I submit each string C, all in one submission to db. Right now I am calling dc.SubmitChanges twice in same call. Is it efficient to have to submit changes twice on same DataContext or can this be combined further?

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• How to render an object tree with paging?

  - by erikzeta

  I’ll render an object graph on a page looking like this: Category 1 Module 1 Product 1 Product 2 Product 3 Module 2 Product 4 Category 2 ... The Category has an IList<Module and the Module contains an IList<Product Now I need to implement paging on this structure but the problem is that I can’t do Category.Skip(page * pageSize).Take(pageSize) because this will only work on the Category object not the whole object tree. In other words I like to render out when the sum of Categories, Modules and Products is equal to the PageSize /erik

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• Fluent Nhibernate expression to select on flagged enum

  - by mbalkema

  I have a domain entity that has a flagged enum as a property. The flagged enum is the target audience for the these entities. The user then has a flagged enum value of the entities they should see. I am trying to figure out the correct expression to select entities that meet the target audience for the user. public class File { public virtual TargetAudience TargetAudience { get; set; } } [Flags] public enum TargetAudience { Audience1 = 1, Audience2 = 2, Audience3 = 4, Audience4 = 8 } Expression: (This works when performed on a IList<File>, but doesn't work on a query to the database.) public Expression<Func<File, bool>> Expression { get { return ((x.TargetAudience & UserTargetedAudience) > 0); } } Any suggestions would be helpful.

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• In Django, I want to insert a database record by sending myself an email?

  - by littlejim84

  Hello. I'm looking into a possible feature for my little to-do application... I like the idea that I can send an email to a particular email address, containing a to-do task I need to complete, and this will be read by my web application and be put in the database... So, when I come to log into my application, the to-do task I emailed will be there as a entry in the app. Is this possible? I have a slice with SliceHost (basically a dedicated server) so I have total control on what to install etc. I'm using Python/Django/MySQL for this. Any ideas on what steps to take to make this happen?

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• problem writing xml to file with .net mvc - timeout?

  - by Mark

  Hey, so having an issue with writing out to an xml file. Works fine for single requests via the browser, but when I use something like Charles to perform 5-10 repeated requests concurrently several of them will fail. The trace simply shows a 500 error with no content inside, basically I think they start timing out waiting for write access or something... This method is inside my repository class, have also attempted to have repository instance as a singleton but doesn't appear to make any difference.. Any help would be much appreciated. Cheers public void Add(Request request) { try { XDocument requests; XmlReader xmlReader; using (xmlReader = XmlReader.Create(_requestsFilePath)) { requests = XDocument.Load(xmlReader); XElement xmlRequest = new XElement("request", new XElement("code", request.code), new XElement("date", request.date), new XElement("email", new XCData(request.email)), new XElement("name", new XCData(request.name)), new XElement("recieveOffers", request.recieveOffers) ); requests.Root.Element("requests").Add(xmlRequest); xmlReader.Close(); } requests.Save(_requestsFilePath); } catch (Exception ex) { HttpContext.Current.Trace.Warn("Error writing to file: "+ex); } }

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• Need help joining tables...

  - by yuudachi

  I am a MySQL newbie, so sorry if this is a dumb question.. These are my tables. student table: SID (primary) student_name advisor (foreign key to faculty.facultyID) requested_advisor (foreign key to faculty.facultyID) faculty table: facultyID (primary key) advisor_name I want to query a table that shows everything in the student table, but I want advisor and requested_advisor to show up as names, not the ID numbers. so like it displays like this on the webpage: Student Name: Jane Smith SID: 860123456 Current Advisor: John Smith Requested advisor: James Smith not like this Student Name: Jane Smith SID: 860123456 Current Advisor: 1 Requested advisor: 2 SELECT student.student_name, SID, student_email, faculty.advisor_name FROM student INNER JOIN faculty ON student.advisor = faculty.facultyID; this comes out close, but I don't know how to get the requested_advisor to show up as a name.

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• optional search parameters in sql query and rows with null values

  - by glenn.danthi

  Ok here is my problem : Before i start the description, let me to tell you that I have googled up a lot and I am posting this question for a good optimal solution :) i am building a rest service on WCF to get userProfiles... the user can filter userProfiles by giving something like userProfiles?location=London now i have the following method GetUserProfiles(string firstname, string lastname, string age, string location) the sql query string i built is: select firstname, lastname, .... from profiles where (firstName like '%{firstname}%') AND (lastName like '%{lastName}%') ....and so on with all variables being replaced by string formatter. Problem with this is that it filters any row having firstname, lastname, age or location having a null value.... doing something like (firstName like '%{firstName}%' OR firstName IS NULL) would be tedious and the statement would become unmaintanable! (in this example there are only 4 arguments, but in my actual method there are 10) What would be the best solution for this?....How is this situation usually handled? Database used : MySql

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• Why don't the classes in the DBML designer appear in alphabetical order?

  - by Mykroft

  I have a DBML file with a very large data model. Whenever I need to add a relationship between to tables I have to select the other table from a combo box which appears to be in in almost random order. Is there a reason these dropdowns aren't in alphabetical order, or is there a way to put them in some kind of order?

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• Should I be concerned about performance with connections to multiple databases?

  - by Josh Ryan

  I have a PHP app that is running on an Apache server with MySQL databases. Based on the subdomain that users access, I am connecting them to a database (sub1.domain.com connects to database_sub1 and sub2.domain.com connects to database_sub2). Right now there are 10 subdomain-database combos, but that number could potentially grow to well over 100. So, is this a bad thing? Considering my situation, is myslq_pconnect a better way to go? Thanks, and please let me know if more info would be helpful. Josh

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• How do I simulate "In" using Linq2Sql

  - by flipdoubt

  I often find myself with a list of disconnected Linq2Sql objects or keys that I need to re-select from a Linq2Sql data-context to update or delete in the database. If this were SQL, I would use IN in the SQL WHERE clause, but I am stuck with what to do in Linq2Sql. Here is a sample of what I would like to write: public void MarkValidated(IList<int> idsToValidate) { using(_Db.NewSession()) // Instatiates new DataContext { // ThatAreIn <- this is where I am stuck var items = _Db.Items.ThatAreIn(idsToValidate).ToList(); foreach(var item in items) item.Validated = DateTime.Now; _Db.SubmitChanges(); } // Disposes of DataContext } Or: public void DeleteItems(IList<int> idsToDelete) { using(_Db.NewSession()) // Instatiates new DataContext { // ThatAreIn <- this is where I am stuck var items = _Db.Items.ThatAreIn(idsToValidate); _Db.Items.DeleteAllOnSubmit(items); _Db.SubmitChanges(); } // Disposes of DataContext } Can I get this done in one trip to the database? If so, how? Is it possible to send all those ints to the database as a list of parameters and is that more efficient than doing a foreach over the list to select each item one at a time?

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• flex actionscript Datagridcolumn array

  - by Jad

  Hi, We have an AIR app and using a datagrid. We want to store the dataGrid.columns array in mySQL DB through PHP. This is needed because the user can customise the column headers of the datagrid and his preference needs to be stored and shown to him on his next login. Using HTTPService, we tried sending the dataGrid.columns array as a string, as follows, var ht:HTTPService = new HTTPService(); ht.url = Config.getServerURL(); ht.method = URLRequestMethod.POST; ht.resultFormat = "text"; ht.request["action"] = "updateGrid"; ht.request["headercolumns"] = colsArray.toString(); The data is stord as comma separated array string in DB. When we retrieve it back, cannot seem to cast it back to the DatagridColumns and assign it. Please let me know. Regards Jada.

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• Entity Framework Duplicate type name within an assembly (6.1.0)

  - by CodeMilian

  I am not sure what is going on but I keep getting the following exception when doing a query. "Duplicate type name within an assembly." I have not been able to find a solution on the web. I had resolved the issue by removing entity framework from all the projects in the solutions and re-installing using nugget. Then all of the sudden the exception is back. I have verified my table schema over and over and find nothing wrong with. This is the query causing the exception. var BaseQuery = from Users in db.Users join UserInstalls in db.UserTenantInstalls on Users.ID equals UserInstalls.UserID join Installs in db.TenantInstalls on UserInstalls.TenantInstallID equals Installs.ID where Users.Username == Username && Users.Password == Password && Installs.Name == Install select Users; var Query = BaseQuery.Include("UserTenantInstalls.TenantInstall"); return Query.FirstOrDefault(); As I mentioned previously the same query was working before. The data has not changed and the code has not changed.

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• Setting property of objects in datacontext

  - by ryudice

  Hi, all my entities have a common property which specifies the company they belong to, I would like to set this property in a method in my datacontext but I do not want to use the partial methods for each of the entity types that the datacontext provides, is there a method that receives any entity that is inserted throught the datacontext so that I can hook to it or override it and set the property using reflection? thanks.

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• Get group key from bridge table

  - by Mads Jensen

  I'm developing an ETL process, and need a bridge table for a one-to-many relationship between a fact table and a dimension table (MySQL database). There is a limited number of combinations (some thousands), so I want to re-use group keys from the bridge table to to limit the size. Any group of dimensions belonging to a fact row will consist of a number of dimension keys (1 to around 15), assigned to a unique group key, as below: group_key | dimension_key ----------------------- 1 | 1 1 | 3 1 | 4 2 | 1 2 | 2 2 | 3 3 | 1 3 | 4 How do I go about retrieving the unique group key for the dimensions 1,3,4 (ie. 1).

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• Updating Linking Tables

  - by Sasha

  I've currently adding a bit of functionality that manages holiday lettings on top of a CMS that runs on PHP and MySQL. The CMS stores the property details on a couple of tables, and I'm adding a third table (letting_times) that will contain information about when people are staying at the property. Basic functionality would allow the user to add new times when a guest is staying, edit the times that the guest is staying and remove the booking if the guest no longer wants to stay at the property. Right now the best way that I can think of updating the times that the property is occupied is to delete all the times contained in the letting_times database and reinsert them again. The only other way that I can think to do this would be to include the table's primary key and do an update if that is present and has a value, otherwise do an insert, but this would not delete rows of data if they are removed. Is there a better way of doing this?

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• LinqToSql: insert instead of update

  - by Christina Mayers

  I am stuck with this problems for a long time now. Everything I try to do is insert a row in my DB if it's new information - if not update the existing one. I've updated many entities in my life before - but what's wrong with this code is beyond me (probably something pretty basic) I guess I can't see the wood for the trees... private Models.databaseDataContext db = new Models.databaseDataContext(); internal void StoreInformations(IEnumerable<EntityType> iEnumerable) { foreach (EntityType item in iEnumerable) { EntityType type = db.EntityType.Where(t => t.Room == iEnumerable.Room).FirstOrDefault(); if (type == null) { db.EntityType.InsertOnSubmit(item); } else { cur.Date = item.Date; cur.LastUpdate = DateTime.Now(); cur.End = item.End; } } } internal void Save() { db.SubmitChanges(); }

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• Problem with SQL syntax (probably simple)

  - by Bryan Folds

  I'm doing some custom database work for a module for Drupal and I get the following SQL error when trying to create my table: user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DEFAULT NULL, rooms INT DEFAULT NULL, adults INT DEFAULT NULL, children' at line 14 query: CREATE TABLE dr_enquiry ( eId INT unsigned NOT NULL auto_increment, eKey VARCHAR(16) NOT NULL, dateSent INT NOT NULL DEFAULT 0, status VARCHAR(30) NOT NULL DEFAULT 'Unanswered', custName VARCHAR(50) NOT NULL, custEmail VARCHAR(200) NOT NULL, custPhone VARCHAR(25) NOT NULL, custCountry VARCHAR(40) NOT NULL, custIP VARCHAR(11) DEFAULT NULL, offerName VARCHAR(100) NOT NULL, offerURL VARCHAR(200) NOT NULL, arrival DATETIME DEFAULT NULL, departure DEFAULT NULL, rooms INT DEFAULT NULL, adults INT DEFAULT NULL, children INT DEFAULT NULL, childAges VARCHAR(32) DEFAULT NULL, toddlers INT DEFAULT NULL, toddlerAges VARCHAR(32) DEFAULT NULL, catering VARCHAR(255) DEFAULT NULL, comments VARCHAR(255) DEFAULT NULL, agent VARCHAR(100) DEFAULT NULL, voucher VARCHAR(100) DEFAULT NULL, PRIMARY KEY (eId) ) /*!40100 DEFAULT CHARACTER SET UTF8 */ in /home/travelco/public_html/includes/database.inc on line 550.

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• Why does this return zero results?

  - by Jon

  I have a List<List<string>> and when I try to search with the List<string> it returns no results. Any ideas? Thanks List<List<string>> test = new List<List<string>>(); List<string> ff = new List<string>(); ff.Add("1"); ff.Add("ABC 1"); test.Add(ff); ff = new List<string>(); ff.Add("2"); ff.Add("ABC 2"); test.Add(ff); var result = test.Where(x=>x.Contains("ABC")); //result.Count(); is 0

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• .Net Reflection - Calling unexisting methods

  - by Joaozinho das Couves

  Lets say i call method M1 on class A using reflection. The method does not exist. Is there any way to put a handler on class A that says, "someone is trying to execute method M1"? Or Is it possible to add a method dinamically to a class? I want to add a method M1...Mn that always does MyStaticClass.DoAction("M1...Mn"); Something like: string methodName = "M1". A.AddMethod(methodname,x = MyStaticClass.DoAction(x)); Thanks

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• Why use Entity Framework over Linq2SQL ...

  - by Refracted Paladin

  To be clear, I am not asking for a side by side comparision which has already been asked Ad Nauseum here on SO. I am also Not asking if Linq2Sql is dead as I don't care. What I am asking is this.... I am building internal apps only for a non-profit organization. I am the only developer on staff. We ALWAYS use SQL Server as our Database backend. I design and build the Databases as well. I have used L2S successfully a couple of times already. Taking all this into consideration can someone offer me a compelling reason to use EF instead of L2S? I was at Code Camp this weekend and after an hour long demonstration on EF, all of which I could have done in L2S, I asked this same question. The speakers answer was, "L2S is dead..." Very well then! NOT! (see here) I understand EF is what MS WANTS us to use in the future(see here) and that it offers many more customization options. What I can't figure out is if any of that should, or does, matter for me in this environment. One particular issue we have here is that I inherited the Core App which was built on 4 different SQL Data bases. L2S has great difficulty with this but when I asked the aforementioned speaker if EF would help me in this regard he said "No!"

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• NullReferenceException in EntityFramework, how come?

  - by Mickel

  Take a look at this query: var user = GetUser(userId); var sessionInvites = ctx.SessionInvites .Include("InvitingUser") .Include("InvitedUser") .Where(e => e.InvitedUser.UserId == user.UserId) .ToList(); var invites = sessionInvites; // Commenting out the two lines below, and it works as expected. foreach (var invite in sessionInvites) ctx.DeleteObject(invite); ctx.SaveChanges(); return invites; Now, everything here executes without any errors. The invites that exists for the user are being deleted and the invites are being returned with success. However, when I then try to navigate to either InvitingUser or InvitedUser on any of the returned invites, I get NullReferenceException. All other properties of the SessionIvites returned, works fine. How come? [EDIT] Now the weird thing is, if I comment out the lines with delete it works as expected. (Except that the entities will not get deleted :S)

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• Is it safe to convert varchar and char into nvarchar and nchar in SQL Server?

  - by Svish

  We currently have a number of columns in the database which are of type varchar. The application that uses them are in C# and it uses Linq2Sql for the communication (or what to call it). We would like to support unicode characters, which means we would have to convert the varchar columns into nvarchar. Is this a safe operation? Is it just a matter of changing the column type and updating the dbml file, or are there more stuff that needs to be done? Any changes in the C# code? Do I need to somehow convert the text that already exist in the database manually, or is it handled for me?

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• Timestamp as int field, query performance

  - by Kirzilla

  Hello, I'm storing timestamp as int field. And on large table it takes too long to get rows inserted at date because I'm using mysql function FROM_UNIXTIME. SELECT * FROM table WHERE FROM_UNIXTIME(timestamp_field, '%Y-%m-%d') = '2010-04-04' Is there any ways to speed this query? Maybe I should use query for rows using timestamp_field >= x AND timestamp_field < y? Thank you I've just tried this query... SELECT * FROM table WHERE timestamp_field >= UNIX_TIMESTAMP('2010-04-14 00:00:00') AND timestamp_field <= UNIX_TIMESTAMP('2010-04-14 23:59:59') but there is no any performance bonuses. :(

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