I have the code below (this is actually part of a much more complicated query, but I have isolated the issue to this particular line to help with debugging) which per everything I have read should create an IN clause in SQL, assuming I am using EF4. As far as I can tell, I am using EF4 (We are using .NET Framework 4 for our projects and when I look at the System.Data and System.Data.Entity they both say version 4.0.0.0 for all the projects)
int[] assessmentIDs; // this is just here to show what this is,
// but it is a params parameter passed to this methed
var assessments = from cert in container.ProctorAssessmentCertifications
where assessmentIDs.Contains(cert.AssessmentID)
select cert.ID;
However, when I run this, I get the runtime error:
LINQ to Entities does not recognize the method 'Boolean Contains[Int32](Int32[], Int32)' method, and this method cannot be translated into a store expression.
When I use LinqPad, it does correctly output an IN clause like one would expect in EF4.
My questions are:
A. What am I doing wrong and how do I make this work?
B. How do I force EF4 to be called if in fact it's not? I can find no reference in any web.config file that point it to the older version.
Contains does not get translated into valid SQL because assessmentIDs is not IQueryable, it is an in-memory object. So you'll have to pull the data out first, and then do the check.
var assessments = (from cert in container.ProctorAssessmentCertifications
select cert.ID).ToList() //no longer IQueryable.
var result = assessments.Intersect(assessmentIDs);
Related
I made a SqlDependency service in my application. It works perfectly when I type the queries by hand but I cannot include wildcards (I don't really know why).
For example:
//Using this SqlCommand will work
new SqlCommand("SELECT [employees].[name] FROM [dbo].[employees]", sqlNotificationConn)
//But this one won't
new SqlCommand("SELECT [employees].* FROM [dbo].[employees]", sqlNotificationConn)
//And this one won't either
new SqlCommand("SELECT * FROM [dbo].[employees]", sqlNotificationConn)
So basically, I want to get my DbContext to generate a full SELECT command with every fields it deals with.
In Linq 2 SQL, I used this service using dbContext.GetCommand(.....);
In EF 4.0 (or was it 4.1?), I used dbContext.employee.ToTraceString();
But in EF 4.4, I can't find anything to generate that SELECT query string....
With DbContext (DbQuery) it is as simple as:
query.ToString()
With ObjectContext (ObjectQuery):
((ObjectQuery)query).ToTraceString()
By the way, query can be any expression based on a DbSet (or ObjectSet, respectively). So something like dbContext.employee.Where(e => e.Name == "Gates").ToString() will also show the generated SQL query.
A LINQ statement that forces execution, like ToList(), Single(), FirstOrDefault(), etc, creates a new object and ToString() will return the object's type name.
ToTraceString() is still in EF, same place it always was. However, it's on ObjectQuery, not DbQuery. Having said that, I've never seen the SQL Server provider for EF use *; it always uses discrete fields in SQL.
None of the many questions on this topic seem to match my situation. I have a large data model. In certain cases, only a few of the fields need be displayed on the UI, so for those I replaced the LINQ to Entity query that pulls in everything with an Entity SQL query retrieving only the columns needed, using a Type constructor so that I got an entity returned and not a DbDataRecord, like this:
SELECT VALUE MyModelNameSpace.INCIDENT(incident.FieldA, incident.FieldB, ...) FROM ... AS ...
This works and displays the fields in the UI. And if I make a change, the change makes it back to the entity model when I tab out of the UI element. But when I do a SaveChanges, the changes do not get persisted to the database. No errors show up in the Log. Now if I very carefully replace the above query with an Entity Sql query that retrieves the entire entity, like this:
SELECT VALUE incident FROM MyDB.INCIDENTs AS incident...
Changes do get persisted in the database! So as a test, I created another query like the first that named every column in the entity, which should be the exact equivalent of the second Entity SQL query. Yet it did not persist changes to the database either.
I've tried setting the MergeOption on the returned result to PreserveChanges, to start tracking, like this:
incidents.MergeOption = MergeOption.PreserveChanges;
But that has no effect. But really, if retrieving the entire entity with Entity Sql persists changes, what logical purpose would there be for behaving differently when a subset of the fields are retrieved? I'm wondering if this is a bug?
Gert was correct, the problem was that the entity was not attached. Dank U wel, Gert! Ik was ervan verbluft!
I just wanted to add a little detail to show the full solution. Basically, the ObjectContext has an Attach method, so you'd think that would be it. However, when your Entity SQL select statement names columns, and you create the object using a Type as I did, the EntityKey is not created, and ObjectContext.Attach fails. After trying and failing to insert the EntityKey I created myself, I stumbled across ObjectSet.Attach, added in Entity Framework 4. Instead of failing, it creates the EntityKey if it is missing. Nice touch.
The code was (this can probably be done in fewer steps, but I know this works):
var QueryString = "SELECT VALUE RunTimeUIDesigner.INCIDENT (incident.INCIDENT_NBR,incident.LOCATION,etc"
ObjectQuery<INCIDENT> incidents = orbcadDB.CreateQuery<INCIDENT>(QueryString);
incidents.MergeOption = MergeOption.PreserveChanges;
List<INCIDENT> retrievedIncidents = incidents.ToList<INCIDENT>();
orbcadDB.INCIDENTs.Attach(retrievedIncidents[0]);
iNCIDENTsViewSource.Source = retrievedIncidents;
I have DbContext (called "MyContext") with about 100 DbSets within it.
Among the domain classes, I have a Document class with 10 direct subclasses (like PurchaseOrder, RequestForQuotation etc).
The heirarchy is mapped with a TPT strategy.
That is, in my database, there is a Document table, with other tables like PurchaseOrder, RequestForQuotation for the subclasses.
When I do a query like:
Document document = myContext.Documents.First();
the query took 5 seconds, no matter whether it's the first time I run it or subsequently.
A query like:
Document document = myContext.Documents.Where(o => o.ID == 2);
also took as long.
Is this an issue with EF4.1 (if so, will EF4.2 help) or is this an issue with the query codes?
Did you try using SQL Profile to see what is actually sent to the DB? It could be that you have too many joins on your Document that are not set to lazy load, and so the query has to do all the joins in one go, bringing back too many columns. Try to send a simple query with just one return column.
As you can read here, there are some performance issues regarding TPT in EF.
The EF Team annouced several fixes in the June 2011 CTP, including TPT queries optimization, but they are not included in EF 4.2, as you can read in the comments to this answer.
In the worst case, these fixes will only be released with .NET 4.5. I'm hoping it will be sooner...
I'm not certain that the DbSet exposed by code-first actually using ObjectQuery but you can try to invoke the .ToTraceString() method on them to see what SQL is generated, like so:
var query = myContext.Documents.Where(o => o.ID == 2);
Debug.WriteLine(query.ToTraceString());
Once you get the SQL you can determine whether it's the query or EF which is causing the delay. Depending on the complexity of your base class the query might include a lot of additional columns, which could be avoided using projection. With using projections, you can perform a query like this:
var query = from d in myContext.Documents
where d.ID == 2
select new
{
o.Id
};
This should basically perform a SELECT ID FROM Documents WHERE ID = 2 query and you can measure how long this takes to gain further information. Of course the projected query might not fit your needs but it might get you on the right track. If this still takes up to 5 seconds you should look into performance problems with the database itself rather than EF.
Update
Apparently with code-first you can use .ToString() instead of .ToTraceString(), thanks Slauma for noticing.
I've just had a 5 sec delay in ExecuteFunction, on a stored procedure that runs instantaneously when called from SQL Management Studio. I fixed it by re-writing the procedure.
It appears that EF (and SSRS BTW) tries to do something like a "prepare" on the stored proc and for some (usually complex) procs that can take a very long time.
A quick and dirty solution is to duplicate and then replace your SP parameters with internal variables:
create proc ListOrders(#CountryID int = 3, #MaxOrderCount int = 20)
as
declare #CountryID1 int, #MaxOrderCount1 int
set #CountryID1 = #CountryID
set #MaxOrderCount1 = #MaxOrderCount
select top (#MaxOrderCount1) *
from Orders
where CountryID = #CountryID1
I'm simply trying to get data from two sql server db tables using ado.net entity framework. My code is:
using (Model.Entities e = new Model.Entities())
{
return e.PAGE.First().CONTROL;
}
The database is setup to have two tables, a control table which links to a page table via an 'id' field in the tables (control_id). There is one CONTROL object for each PAGE object.
I keep getting a null value for my return value and I know that's not right.
I can use vis studio and breakpoints to see that there is a PAGE object in 'e' and I can see that there are multiple CONTROL objects in 'e'. This isn't a large database, I just have some sample data in there to ensure that I get this working - so I know that there should be a CONTROL object connected to this PAGE (i've verified this through sql server).
I am very familiar with the general code syntax, I've been using LINQ for a couple of years; however, I have not done much work at all with the entity framework or ado.net 4.
It seems like if I just pull individual table data then it works fine (i.e. e.PAGE.First() .. or .. e.CONTROL.Where(x=>x.someValue.Equals('someValue') ) but if I try to pull by traversing through the tables then I get nothing back (NULL).
Hope that all makes sense.
Some questions for you:
I assume is a 1..1 between PAGE and CONTROL,
Is there a FK called "ControlID" on PAGE?
Do you have a navigational property called "Control" on your "Page" entity in your EDMX?
If the answer to all of the above is Yes, then this should work:
var page = e.Pages.Include("Control").First();
Here, you are returning the First "Page" record, and eager loading the associated control.
The SQL produced should be something like this:
SELECT p.*, c.*
FROM Page p
INNER JOIN Control c
on p.ControlId = c.ControlId
I have a SQL Server 2008 database. I have a bunch of fields in TableA that are just strings that corresponds to booleans. So every value is either true or false. The edmx I generated using Entity Framework 4.0 has them as strings. This is technically correct but I would like to have them mapped as Booleans instead. Is this possible? If so how can I accomplish this?
Thanks much!
You could create a partial class alongside the generated one and add the bool property there with code to go back and forth from bool to string version. You could also mark the generated property as protected or internal to hide it from the rest of your code.
It's not ideal since the bool property cannot appear in query expressions unless you first force the query to happen using, for example, .ToList().
Your best bet would be to fix the database.