LINQ Dynamic Where - Not adding clause

Question

I have the following code:

public OTestTable GetTestCode(Func<TestTable, bool> whereClause)
{
    return CoreContext.TestTables.Where(whereClause).Select(TestTableMap.DataToObject).FirstOrDefault();
}

CoreContext is my data context (which is initialized in a base class)

My TestTableMap is as follows:

public class TestTableMap
{
    public static readonly Func<TestTable, OTestTable> DataToObject = mapper =>
       new OTestTable
       {
           Code = mapper.mycode 

       };
}

Then in my business method i have the following:

public OTestTable GetTestCode(string code)
{
    return QueryEngine.GetTestCode(id => id.mycode == code);
}

From my main program, i am calling GetTestCode with a string value.

When I watch SQL profiler, I get the following:

SELECT [t0].[mycode]
FROM [dbo].[TestTable] AS [t0]

It does not have the where clause appended to the SQL query. If i add the where clause to the LINQ as var query = from c in DataContext.TestTable where c.mycode == '' select c;

It will add the where clause.

However, when I run my code, it will return the correct record, but it seems like I am pulling back all records from the database and filtering in my code (which should not happen).

Any thoughts with what I am doing wrong?

Thanks

Christian Hayter · Accepted Answer · 2009-11-30 20:02:53Z

3

In order to construct SQL statements, LINQ to SQL requires an expression tree. Func<TestTable, bool> does not represent an expression tree, it is a "black box" function pointer. LINQ cannot do anything intelligent with this apart from blindly execute it on an in-memory collection.

You need to do this instead:

public OTestTable GetTestCode(Expression<Func<TestTable, bool>> whereClause) {
    return CoreContext.TestTables.Where(whereClause).Select(TestTableMap.DataToObject).FirstOrDefault();
}

This code compiles using the Queryable.Where extension method, which does accept an expression tree, rather than the Enumerable.Where extension method, which only accepts a raw delegate.

edited Nov 30, 2009 at 20:02

answered Nov 30, 2009 at 19:57

Christian Hayter

31.2k6 gold badges76 silver badges101 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

CodeLikeBeaker Over a year ago

that was it!! I totally forgot about using the Expression!! Thanks a bunch!

flesh · Accepted Answer · 2009-11-30 20:00:41Z

2

Try creating your where clause as:

Expression<Func<T, bool>> whereClause

Where the T parameter is your source type Table<T> source

answered Nov 30, 2009 at 20:00

flesh

23.9k24 gold badges83 silver badges99 bronze badges

Comments

Gongdo Gong · Accepted Answer · 2015-04-02 13:06:19Z

0

Also see the PredicateBuilder here: http://www.albahari.com/nutshell/predicatebuilder.aspx

It provides you convenient extension methods to predicate IQueryable<T>. like this:

var predicate = PredicateBuilder.True<Family>();
predicate = predicate.And(o => o.Birthday < new DateTime(1980, 1, 1));
                     .Or(o => o.Name.Contains("ke"));
var result = Source.Where(predicate).ToList();

answered Apr 2, 2015 at 13:06

Gongdo Gong

1,0289 silver badges18 bronze badges

Collectives™ on Stack Overflow

LINQ Dynamic Where - Not adding clause

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related