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• SQL vs MySQL: Rules about aggregate operations and GROUP BY

  - by Phazyck

  In this book I'm currently reading while following a course on databases, the following example of an illegal query using an aggregate operator is given: Find the name and age of the oldest sailor. Consider the following attempt to answer this query: SELECT S.name, S.age FROM Sailors.S The intent is for this query to return not only the maximum age but also the name of the sailors having that age. However, this query is illegal in SQL--if the SELECT clause uses an aggregate operation, then it must use only aggregate operations unless the query contains a GROUP BY clause! Some time later while doing an exercise using MySQL, I faced a similar problem, and made a mistake similar to the one mentioned. However, MySQL didn't complain and just spit out some tables which later turned out not be what I needed. Is the query above really illegal in SQL, but legal in MySQL, and if so, why is that? In what situation would one need to make such a query?

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• MySQL: filling empty fields with zeroes when using GROUP BY

  - by SaltLake

  I've got MySQL table CREATE TABLE cms_webstat ( ID int NOT NULL auto_increment PRIMARY KEY, TIMESTAMP_X timestamp DEFAULT CURRENT_TIMESTAMP, # ... some other fields ... ) which contains statistics about site visitors. For getting visits per hour I use SELECT hour(TIMESTAMP_X) as HOUR , count(*) AS HOUR_STAT FROM cms_webstat GROUP BY HOUR ORDER BY HOUR DESC which gives me | HOUR | HOUR_STAT | | 24 | 15 | | 23 | 12 | | 22 | 9 | | 20 | 3 | | 18 | 2 | | 15 | 1 | | 12 | 3 | | 9 | 1 | | 3 | 5 | | 2 | 7 | | 1 | 9 | | 0 | 12 | And I'd like to get following: | HOUR | HOUR_STAT | | 24 | 15 | | 23 | 12 | | 22 | 9 | | 21 | 0 | | 20 | 3 | | 19 | 0 | | 18 | 2 | | 17 | 0 | | 16 | 0 | | 15 | 1 | | 14 | 0 | | 13 | 0 | | 12 | 3 | | 11 | 0 | | 10 | 0 | | 9 | 1 | | 8 | 0 | | 7 | 0 | | 6 | 0 | | 5 | 0 | | 4 | 0 | | 3 | 5 | | 2 | 7 | | 1 | 9 | | 0 | 12 | How should I modify the query to get such result? Thanks.

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• Getting counts of 0 from a query with a double group by

  - by Maltiriel

  I'm trying to write a query that gets the counts for a table (call it item) categorized by two different things, call them type and code. What I'm hoping for as output is the following: Type Code Count 1 A 3 1 B 0 1 C 10 2 A 0 2 B 13 2 C 2 And so forth. Both type and code are found in lookup tables, and each item can have just one type but more than one code, so there's also a pivot (aka junction or join) table for the codes. I have a query that can get this result: Type Code Count 1 A 3 1 C 10 2 B 13 2 C 2 and it looks like (with join conditions omitted): SELECT typelookup.name, codelookup.name, COUNT(item.id) FROM typelookup LEFT OUTER JOIN item JOIN itemcodepivot RIGHT OUTER JOIN codelookup GROUP BY typelookup.name, codelookup.name Is there any way to alter this query to get the results I'm looking for? This is in MySQL, if that matters. I'm not actually sure this is possible all in one query, but if it is I'd really like to know how. Thanks for any ideas.

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• Do you know of a C dictionary that supports COW transactions?

  - by Tim Post

  I'm looking for a key - value dictionary library written in C that supports a theoretically unlimited number of cheap transactions. I'd like to have one dictionary in memory, with hundreds of threads starting transactions, possibly modifying the dictionary, ending (completing) the transaction or potentially aborting the transaction. Only 50% of the time will these threads actually modify the dictionary. Most dictionary transaction implementations that I've seen copy always, instead of copying on write, whenever a transaction is started. Given the expected size ( 1GB) of the dictionary, I'm hoping to find something that COWs only when something is actually changed during a transaction. I'm also hoping for something that is packaged by most major GNU/Linux distributions. Any suggestions or links are very much appreciated.

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• how to select and group mysql data based on the follwoing table

  - by user1151680

  how can I achieve the desired result in mysql if my table looks like this. result|year 1 |2011 2 |2011 1 |2011 0 |2011 1 |2012 2 |2012 1 = Won, 2 = lost, 0 = draw Every year can have multiple values like this. Not sure how I can get the desired result like below. year won lost draw totalPlayed 2011 2 1 1 3 2012 1 1 0 2 I have tried the following query but does not get the desired result select year, league_types.league_name, sum(if(result = 1,1,0)) as won, sum(if(result = 0,1,0)) as draw, sum(if(result = 4,1,0)) as noResult, sum(if(result = 2,1,0)) as lost, sum(if(result = 3,1,0)) as tied, sum(if(result > 0 and result < 4,1,0)) as played from match_score_card inner join fixtures on match_score_card.match_id = fixtures.match_id inner join league_types on fixtures.league_id = league_types.league_id where team_id = 1 group by year order by year desc

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• Working by group by for grouping data into string format

  - by Shantanu Gupta

  I have a table that contains some data given below. It uses a tree like structure i.e. Department SubD1, SubD2 ..... PreSubD1, PreSubD1... PreSubD2, PreSubD2... pk_map_id preferences ImmediateParent Department_Id -------------------- -------------------- -------------------- -------------------- 20 14 5 1 21 15 5 1 22 16 6 1 23 9 4 2 24 4 3 2 25 24 20 2 26 25 20 2 27 23 13 2 I want to group my records on behalf of department then immediate parent then preferences each seperated by ',' i.e. department Immediate Parent preferences 1 5,6 14,15,16 2 4,3,20,13 9,4,24,25,23 and this table also Immediate parent preferences 5 14,15 6 16 4 9 3 4 20 24,25 13 13 In actual scenario all these are my ids which are to be replaced by their string fields. I am using sql server 2k5

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• MySQL query with JOINS and GROUP BY

  - by user1854049

  I'm building a MySQL query but I can't seem to get it right. I have four tables: - customers - orders - sales_rates - purchase_rates There is a 1:n relation 'customernr' between customers and orders. There is a 1:n relation 'ordernr' between orders and sales_rates. There is a 1:n relation 'ordernr' between orders and purchase_rates. What I would like to do is produce an output of all customers with their total purchase and sales amounts. So far I have the following query. SELECT c.customernr, c.customer_name, SUM(sr.sales_price) AS sales_price, SUM(pr.purchase_price) AS purchase_price FROM orders o, customers c, sales_rates sr, purchase_rates pr WHERE o.customernr = c.customernr AND o.ordernr = sr.ordernr AND o.ordernr = pr.ordernr GROUP BY k.bedrijfsnaam The result of the sales_price and purchase_price is far too high. I seem to be getting double counts. What am I doing wrong? Is it possible to perform this in a single query? Thank for your response!

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• Oracle Group By Issue

  - by m_oLogin

  Hello community, I am strugling with what seems an easy problem to tackle (at least for me in MySQL / SqlServer!) I'll simplify the problem. Let's say I have the following table: Table VOTE ID ID_IDEA DATE_VOTE with ID_IDEA FK(IDEA.ID) 1 3 10/10/10 2 0 09/09/10 3 3 08/08/10 4 3 11/11/10 5 0 06/06/10 6 1 05/05/10 I'm trying to find the latest votes given for each individual idea, meaning I want to return only rows with ID 4, 2 and 6. It seems with Oracle that you can't use GROUP BY without using a function like SUM(), AVG, etc. I'm a bit confused about how it's supposed to work. Please advise, Thanks.

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• Oracle Utilities Application Framework V4.1 Group Fix 4 available

  - by ACShorten

  Oracle Utilities Application Framework V4.1 Group Fix 4 is available from My Oracle Support as Patch 13523301. This Group Fix contains a number of enhancements and keeps fixes up to date to the latest patch level. The enhancements included in this Group Fix include: UI Hints - In previous group fixes of the Oracle Utilities Application Framework the infrastructure to support UI Hints was introduced. This group fix completes the release of this functionality. Prior to this enhancement, products and implementers typically would build at least one UI Map per Business Object to display and/or maintain the object. Whilst, this can be generated using the UI Map maintenance function and stored, this enhancement allows additional tags and elements to be added to the Business Object directly to allow dynamic generation of the UI Map for maintenance and viewing the object. This reduces the need to generate and build a UI Map at all for that object. This will reduce maintenance effort of maintaining the product and implementation by eliminating the need to maintain the HTML for the UI Map. This also allows lower skilled personnel to maintain the system. Help and working examples are available from the View schema attributes and node names option from the Schema Tips dashboard zone. For example: Note: For examples of the hints, refer to an of the following Business Objects F1_OutcomeStyleLookup, F1-TodoSumEmailType, F1-BOStatusReason or F1-BIGeneralMasterConfig. Setting batch log file names -  By default the batch infrastructure supplied with the Oracle Utilities Application Framework sets the name and location of the log files to set values. In Group Fix 4 a set of user exits have been added to allow implementers and partners to set their own filename and location.  Refer to the Release Notes in the download for more details.

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• Setting up group disk quotas

  - by Ray

  I am hoping to get some advice in setting up disk quotas. So, I know about: Adding usrquota and grpquota on to /etc/fstab for the file systems that need to be managed. Using edquota to assign disk quotas to users. However, I need to do the last step for multiple users and edquota seems to be a bit troublesome. One solution that I have found is that I can do: sudo edquota -u foo -p bar. This will copy the disk quota of bar to user foo. I was wondering if this is the best solution? I tried setting up group disk quotas but they don't seem to be working. Are group quotas meant to help in the assignment of the same quota to multiple users? Or are they suppose to give a total limit to a set of users? For example, if users A, B, C are in group X then assigning a quota of 20 GB gives each user 20 GB or does it give 20 GB to the entire group X to divide up? I'm interested in doing the former, but not the latter. Right now, I've assigned group disk quotas and they aren't working. So, I guess it is due to my misunderstanding of group disk quotas... My problem is I want to easily give the same quota to multiple users; any suggestions on the best way to do this out of what I've tried above or anything else I may not have thought of? Thank you!

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• bulk insert and update with ADO.NET Entity Framework

  - by Keith Barrows

  I am writing a small application that does a lot of feed processing. I want to use LINQ EF for this as speed is not an issue, it is a single user app and, in the end, will only be used once a month. My questions revolves around the best way to do bulk inserts using LINQ EF. After parsing the incoming data stream I end up with a List of values. Since the end user may end up trying to import some duplicate data I would like to "clean" the data during insert rather than reading all the records, doing a for loop, rejecting records, then finally importing the remainder. This is what I am currently doing: DateTime minDate = dataTransferObject.Min(c => c.DoorOpen); DateTime maxDate = dataTransferObject.Max(c => c.DoorOpen); using (LabUseEntities myEntities = new LabUseEntities()) { var recCheck = myEntities.ImportDoorAccess.Where(a => a.DoorOpen >= minDate && a.DoorOpen <= maxDate).ToList(); if (recCheck.Count > 0) { foreach (ImportDoorAccess ida in recCheck) { DoorAudit da = dataTransferObject.Where(a => a.DoorOpen == ida.DoorOpen && a.CardNumber == ida.CardNumber).First(); if (da != null) da.DoInsert = false; } } ImportDoorAccess newIDA; foreach (DoorAudit newDoorAudit in dataTransferObject) { if (newDoorAudit.DoInsert) { newIDA = new ImportDoorAccess { CardNumber = newDoorAudit.CardNumber, Door = newDoorAudit.Door, DoorOpen = newDoorAudit.DoorOpen, Imported = newDoorAudit.Imported, RawData = newDoorAudit.RawData, UserName = newDoorAudit.UserName }; myEntities.AddToImportDoorAccess(newIDA); } } myEntities.SaveChanges(); } I am also getting this error: System.Data.UpdateException was unhandled Message="Unable to update the EntitySet 'ImportDoorAccess' because it has a DefiningQuery and no element exists in the element to support the current operation." Source="System.Data.SqlServerCe.Entity" What am I doing wrong? Any pointers are welcome.

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• InvalidOperationException when calling SaveChanges in .NET Entity framework

  - by Pär Björklund

  Hi, I'm trying to learn how to use the Entity framework but I've hit an issue I can't solve. What I'm doing is that I'm walking through a list of Movies that I have and inserts each one into a simple database. This is the code I'm using private void AddMovies(DirectoryInfo dir) { MovieEntities db = new MovieEntities(); foreach (DirectoryInfo d in dir.GetDirectories()) { Movie m = new Movie { Name = d.Name, Path = dir.FullName }; db.AddToMovies(movie); } db.SaveChanges(); } When I do this I get an exception at db.SaveChanges() that read. The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges. I haven't been able to find out what's causing this issue. My database table contains three columns Id int autoincrement Name nchar(255) Path nchar(255) Update: I Checked my edmx file and the SSDL section have the StoreGeneratedPattern="Identity" as suggested. I also followed the blog post and tried to add ClientAutoGenerated="true" and StoreGenerated="true" in the CSDL as suggested there. This resulted in compile errors ( Error 5: The 'ClientAutoGenerated' attribute is not allowed.). Since the blog post is from 2006 and it has a link to a follow up post I assume it's been changed. However, I cannot read the followup post since it seems to require an msdn account.

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• entity framework 4 POCO's stored procedure error - "The FunctionImport could not be found in the container"

  - by user331884

  Entity Framework with POCO Entities generated by T4 template. Added Function Import named it "procFindNumber" specified complex collection named it "NumberResult". Here's what got generated in Context.cs file: public ObjectResult<NumberResult> procFindNumber(string lookupvalue) { ObjectParameter lookupvalueParameter; if (lookupvalue != null) { lookupvalueParameter = new ObjectParameter("lookupvalue", lookupvalue); } else { lookupvalueParameter = new ObjectParameter("lookupvalue", typeof(string)); } return base.ExecuteFunction<NumberResult>("procFindNumber", lookupvalueParameter); } Here's the stored procedure: ALTER PROCEDURE [dbo].[procFindNumber] @lookupvalue varchar(255) AS BEGIN SET NOCOUNT ON; DECLARE @sql nvarchar(MAX); IF @lookupvalue IS NOT NULL AND @lookupvalue <> '' BEGIN SELECT @sql = 'SELECT dbo.HBM_CLIENT.CLIENT_CODE, dbo.HBM_MATTER.MATTER_NAME, dbo.HBM_MATTER.CLIENT_MAT_NAME FROM dbo.HBM_MATTER INNER JOIN dbo.HBM_CLIENT ON dbo.HBM_MATTER.CLIENT_CODE = dbo.HBM_CLIENT.CLIENT_CODE LEFT OUTER JOIN dbo.HBL_CLNT_CAT ON dbo.HBM_CLIENT.CLNT_CAT_CODE = dbo.HBL_CLNT_CAT.CLNT_CAT_CODE LEFT OUTER JOIN dbo.HBL_CLNT_TYPE ON dbo.HBM_CLIENT.CLNT_TYPE_CODE = dbo.HBL_CLNT_TYPE.CLNT_TYPE_CODE WHERE (LTRIM(RTRIM(dbo.HBM_MATTER.CLIENT_CODE)) <> '''')' SELECT @sql = @sql + ' AND (dbo.HBM_MATTER.MATTER_NAME like ''%' + @lookupvalue + '%'')' SELECT @sql = @sql + ' OR (dbo.HBM_MATTER.CLIENT_MAT_NAME like ''%' + @lookupvalue + '%'')' SELECT @sql = @sql + ' ORDER BY dbo.HBM_MATTER.MATTER_NAME' -- Execute the SQL query EXEC sp_executesql @sql END END In my WCF service I try to execute the stored procedure: [WebGet(UriTemplate = "number/{value}/?format={format}")] public IEnumerable<NumberResult> GetNumber(string value, string format) { if (string.Equals("json", format, StringComparison.OrdinalIgnoreCase)) { WebOperationContext.Current.OutgoingResponse.Format = WebMessageFormat.Json; } using (var ctx = new MyEntities()) { ctx.ContextOptions.ProxyCreationEnabled = false; var results = ctx.procFindNumber(value); return results.ToList(); } } Error message says "The FunctionImport ... could not be found in the container ..." What am I doing wrong?

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• JavaScriptSerializer().Serialize(Entity Framework object)

  - by loviji

  May be, it is not so problematic for you. but i'm trying first time with json serialization. and also read other articles in stackowerflow. I have created Entity Framework data model. then by method get all data from object: private uqsEntities _db = new uqsEntities(); //get all data from table sysMainTableColumns where tableName=paramtableName public List<sysMainTableColumns> getDataAboutMainTable(string tableName) { return (from column in _db.sysMainTableColumns where column.TableName==tableName select column).ToList(); } my webservice: public string getDataAboutMainTable() { penta.DAC.Tables dictTable = new penta.DAC.Tables(); var result = dictTable.getDataAboutMainTable("1"); return new JavaScriptSerializer().Serialize(result); } and jQuery ajax method $('#loadData').click(function() { $.ajax({ type: "POST", url: "WS/ConstructorWS.asmx/getDataAboutMainTable", data: "{}", contentType: "application/json; charset=utf-8", dataType: "json", success: function(msg) { $("#jsonResponse").html(msg); var data = eval("(" + msg + ")"); //do something with data }, error: function(msg) { } }); }); problem with data, code fails there. and i think i'm not use JavaScriptSerializer().Serialize() method very well. Please, tell me, what a big mistake I made in C# code?

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• Entity Framework 4 Code First and the new() Operator

  - by Eric J.

  I have a rather deep hierarchy of objects that I'm trying to persist with Entity Framework 4, POCO, PI (Persistence Ignorance) and Code First. Suddenly things started working pretty well when it dawned on me to not use the new() operator. As originally written, the objects frequently use new() to create child objects. Instead I'm using my take on the Repository Pattern to create all child objects as needed. For example, given: class Adam { List<Child> children; void AddChildGivenInput(string input) { children.Add(new Child(...)); } } class Child { List<GrandChild> grandchildren; void AddGrandChildGivenInput(string input) { grandchildren.Add(new GrandChild(...)); } } class GrandChild { } ("GivenInput" implies some processing not shown here) I define an AdamRepository like: class AdamRepository { Adam Add() { return objectContext.Create<Adam>(); } Child AddChildGivenInput(Adam adam, string input) { return adam.children.Add(new Child(...)); } GrandChild AddGrandchildGivenInput(Child child, string input) { return child.grandchildren.Add(new GrandChild(...)); } } Now, this works well enough. However, I'm no longer "ignorant" of my persistence mechanism as I have abandoned the new() operator. Additionally, I'm at risk of an anemic domain model since so much logic ends up in the repository rather than in the domain objects. After much adieu, a question: Or rather several questions... Is this pattern required to work with EF 4 Code First? Is there a way to retain use of new() and still work with EF 4 / POCO / Code First? Is there another pattern that would leave logic in the domain object and still work with EF 4 / POCO / Code First? Will this restriction be lifted in later versions of Code First support? Sometimes trying to go the POCO / Persistence Ignorance route feels like swimming upstream, other times it feels like swimming up Niagra Falls.

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• Autonumber with Entity Framework

  - by dcompiled

  I want to loop through a collection of objects and add them all to a table. The destination table has an auto-increment field. If I add a single object there is no problem. If I add two objects both with the primary key of zero, the entity framework fails. I can manually specify primary keys but the whole point of trying the EF was to make life easier not more complicated. Here is the code and the exception received follows. foreach (Contact contact in contacts) { Instructor instructor = InstructorFromContact(contact); context.AddToInstructors(instructor); } try { context.SaveChanges(); } catch (Exception ex) { Console.WriteLine(ex.ToString()); } System.InvalidOperationException: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges. at System.Data.Objects.ObjectContext.SaveChanges(SaveOptions options) at System.Data.Objects.ObjectContext.SaveChanges() at DataMigration.Program.CopyInstructors() in C:\Projects\DataMigration\Program.cs:line 52

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• Problem with cascade delete using Entity Framework and System.Data.SQLite

  - by jamone

  I have a SQLite DB that is set up so when I delete a Person the delete is cascaded. This works fine when I manually delete a Person (all records that reference the PersonID are deleted). But when I use Entity Framework to delete the Person I get an error: System.InvalidOperationException: The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted. I don't understand why this is occurring. My trigger is set to clean up all related objects before deleting the object it was told to delete. When I go into the model editor and check the properties of the relationship it shows no action for the OnDelete property. Why isn't this set correctly by pulling it from the DB? If I change this value to Cascade everything works properly, but I would rather not rely on this manual change because what if I refresh my model from the DB and it looses that. Here's the relivent SQL for my tables. CREATE TABLE [SomeTable] ( [SomeTableID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, [PersonID] INTEGER NOT NULL REFERENCES [Person](PersonID) ON DELETE CASCADE ) CREATE TABLE [Person] ( [PersonID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT )

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• Problem deleting record using Entity Framework and System.Data.SQLite

  - by jamone

  I have a SQLite DB that is set up so when I delete a Person the delete is cascaded. This works fine when I manually delete a Person (all records that reference the PersonID are deleted). But when I use Entity Framework to delete the Person I get an error: System.InvalidOperationException: The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted. I don't understand why this is occurring. My trigger is set to clean up all related objects before deleting the object it was told to delete. When I go into the model editor and check the properties of the relationship it shows no action for the OnDelete property. Why isn't this set correctly by pulling it from the DB? Here's the relivent SQL for my tables. CREATE TABLE [SomeTable] ( [SomeTableID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, [PersonID] INTEGER NOT NULL REFERENCES [Person](PersonID) ON DELETE CASCADE ) CREATE TABLE [Person] ( [PersonID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT )

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• Entity Framework, Foreign Keys and EntityKeys

  - by Greg

  I've got a problem with the Entity Framework and the ForeignKeys. I've got a table "BC_Message_Assets" which has 3 FK's (MessageId, AssetId and StatusId). I create my "MessageAsset" like this MessageAsset messageAsset = new MessageAsset(); messageAsset.MessageStatusReference.EntityKey = new EntityKey("MyEntities.MessageStatusSet", "Id", 1); messageAsset.AssetReference.EntityKey = new EntityKey("MyEntities.AssetSet", "Id", 1); messageAsset.MessageReference.EntityKey = new EntityKey("MyEntities.MessageSet", "Id", messageId); context.AddToMessageAssetSet(messageAsset); context.SaveChanges(); But I got the following exception : The INSERT statement conflicted with the FOREIGN KEY constraint \"FK_BC_Message_Assets_BC_Assets\". The conflict occurred in database \"Test\", table \"dbo.BC_Assets\", column 'Id'.\r\nThe statement has been terminated. When I look at the query, I notice that the parameter value for AssetId is "0" despite that I provided "1" to the EntityKey. Here's the generated query : exec sp_executesql N'insert [dbo].[BC_Message_Assets]([MessageId], [AssetId], [CompletionTime], [StatusId]) values (@0, @1, null, @2) ',N'@0 int,@1 int,@2 int',@0=47,@1=0,@2=1 I can't explain what happens. I hardcoded "1" in the EntityKey and I received "0" in the query ?

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• Entity Framework query not returning correctly enumerated results.

  - by SkippyFire

  I have this really strange problem where my entity framework query isn't enumerating correctly. The SQL Server table I'm using has a table with a Sku field, and the column is "distinct". It isn't a key, but it doesn't contain any duplicate values. Using actual SQL with where, distinct and group by cluases I have confirmed this. However, when I do this: // Not good foreach(var product in dc.Products) or // Not good foreach(var product in dc.Products.ToList()) or // Not good foreach(var product in dc.Products.OrderBy(p => p.Sku)) the first two objects that are returned ARE THE SAME!!! The third item was technically the second item in the table, but then the fourth item was the first row from the table again!!! The only solution I have found is to use the Distinct extension method, which shouldn't really do anything in this situation: // Good foreach(var product in dc.Products.ToList().Distinct()) Another weird thing about this is that the count of the resulting queries is the same!!! So whether or not the resulting enumerable has the correct results or duplicates, I always get the number of rows in the actual table! (No I don't have a limit clause anywhere). What could possibly cause this!?!?!?

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• entity framework POCO template in a n-tiers design question

  - by bryan

  HI all I was trying to follow the POCO Template walkthrough . And now I am having problems using it in n-tiers design. By following the article, I put my edmx model, and the template generated context.tt in my DAL project, and moved the generated model.tt entity classes to my Business Logic layer (BLL) project. By doing this, I could use those entities inside my BLL without referencing the DAL, I guess that is the idea of PI; without knowing anything about the data source. Now, I want to extend the entities (inside the model.tt) to perform some CUD action in the BLL project,so I added a new partial class same name as the one generated from template, public partial class Company { public static IEnumerable AllCompanies() { using(var context = new Entities()){ var q = from p in context.Companies select p; return q.ToList(); } } } however visual studio won't let me do that, and I think it was because the context.tt is in the DAL project, and the BLL project could not add a reference to the DAL project as DAL has already reference to the BLL. So I tried to added this class to the DAL and it compiled, but intelisense won't show up the BLL.Company.AllCompanies() in my web service method from my webservice project which has reference to my BLL project. What should I do now? I want to add CUD methods to the template generated entities in my BLL project, and call them in my web services from another project. I have been looking for this answer a few days already, and I really need some guides from here please. Bryan

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• Entity Framework lazy loading doesn't work from other thread

  - by Thomas Levesque

  Hi, I just found out that lazy loading in Entity Framework only works from the thread that created the ObjectContext. To illustrate the problem, I did a simple test, with a simple model containing just 2 entities : Person and Address. Here's the code : private static void TestSingleThread() { using (var context = new TestDBContext()) { foreach (var p in context.Person) { Console.WriteLine("{0} lives in {1}.", p.Name, p.Address.City); } } } private static void TestMultiThread() { using (var context = new TestDBContext()) { foreach (var p in context.Person) { Person p2 = p; // to avoid capturing the loop variable ThreadPool.QueueUserWorkItem( arg => { Console.WriteLine("{0} lives in {1}.", p2.Name, p2.Address.City); }); } } } The TestSingleThread method works fine, the Address property is lazily loaded. But in TestMultiThread, I get a NullReferenceException on p2.Address.City, because p2.Address is null. It that a bug ? Is this the way it's supposed to work ? If so, is there any documentation mentioning it ? I couldn't find anything on the subject on MSDN or Google... And more importantly, is there a workaround ? (other than explicitly calling LoadProperty from the worker thread...) Any help would be very appreciated PS: I'm using VS2010, so it's EF 4.0. I don't know if it was the same in the previous version of EF...

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• C# Entity FrameWork MySQL Slow Queries Count()

  - by Matthew M.

  Hello, I'm having a serious issue with MySQL and Entity Framework 4.0. I have dropped a Table onto the EF Designer surface, and everything seems OK. However, when I perform a query in the following fashion: using(entityContext dc = new entityContext()) { int numRows = dc.myTable.Count(); } The query that is generated looks something like this: SELECT `GroupBy1`.`A1` AS `C1` FROM (SELECT Count(1) AS `A1` FROM (SELECT `pricing table`.`a`, `pricing table`.`b`, `pricing table`.`c`, `pricing table`.`d`, `pricing table`.`e`, `pricing table`.`f`, `pricing table`.`g`, `pricing table`.`h`, `pricing table`.`i` FROM `pricing table` AS `pricing table`) AS `Extent1`) AS `GroupBy1` As should be evident, this is an excruciatingly unoptimized query. It is selecting every single row! This is not optimal, nor is it even possible for me to use MySQL + EF at this point. I have tried both the MySQL 6.3.1 [that was fun to install] and DevArt's dotConnect for MySQL and both produce the same results. This table has 1.5 million records.. and takes 6-11s to execute! What am I doing wrong ? Is there any way to optimize this [and other queries] to produce sane code like: SELECT COUNT(*) FROM table ? Generating the same query using SQLServer takes virtually no time and produces sane code. Help! Thanks! Matthew

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• Help me understand entity framework 4 caching for lazy loading

  - by Chris

  I am getting some unexpected behaviour with entity framework 4.0 and I am hoping someone can help me understand this. I am using the northwind database for the purposes of this question. I am also using the default code generator (not poco or self tracking). I am expecting that anytime I query the context for the framework to only make a round trip if I have not already fetched those objects. I do get this behaviour if I turn off lazy loading. Currently in my application I am breifly turning on lazy loading and then turning it back off so I can get the desired behaviour. That pretty much sucks, so please help. Here is a good code example that can demonstrate my problem. Public Sub ManyRoundTrips() context.ContextOptions.LazyLoadingEnabled = True Dim employees As List(Of Employee) = context.Employees.Execute(System.Data.Objects.MergeOption.AppendOnly).ToList() 'makes unnessesary round trip to the database, I just loaded the employees' MessageBox.Show(context.Employees.Where(Function(x) x.EmployeeID < 10).ToList().Count) context.Orders.Execute(System.Data.Objects.MergeOption.AppendOnly) For Each emp As Employee In employees 'makes unnessesary trip to database every time despite orders being pre loaded.' Dim i As Integer = emp.Orders.Count Next End Sub Public Sub OneRoundTrip() context.ContextOptions.LazyLoadingEnabled = True Dim employees As List(Of Employee) = context.Employees.Include("Orders").Execute(System.Data.Objects.MergeOption.AppendOnly).ToList() MessageBox.Show(employees.Where(Function(x) x.EmployeeID < 10).ToList().Count) For Each emp As Employee In employees Dim i As Integer = emp.Orders.Count Next End Sub Why is the first block of code making unnessesary round trips?

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• Entity Framework and stored procedure returning temp table Issues

  - by kaplooeymom

  (Disclaimer - I'm not the database designer. I'm just the poor developer what has to make this work.) There are 17 (at the moment) tables with identical structure - name, address, phone number. Given a phone number, I have to check to see if there's a matching entry in any of the tables, then return that address. So, I created a view to get the list of tables (there's a ref table that holds that info), then I created a stored procedure to create a temp table, using cursors, check each table in the view for the phone number, using sql concatenation. If a record is found, insert it into the temp table. return the rows from the temp table. This all works in straight T-SQL. Now, I'm trying to use Entity Framework 4+ to call the stored procedure. But the function import interface won't generate columns. It says return type = none, and the LINQ code expects an int and won't compile. Any ideas on how to make this work? I know I can move the check tables part to code, if I absolutely have to, but I'd rather have the above method work.

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