Question

I am trying to chain multiple compiled linq queries together. I have succeeded in chaining two queries together, but I cannot get a chain of three to work correctly. So here is a reduction of my code to recreate the issue. My two questions are: ‘Why isn’t this working?’ and ‘Is there a better way to keep the performance benefit of compiled queries and also avoid duplication of base query logic that is commonly used?’

Define the following two queries:

Func<DataContext, IQueryable<User>> selectUsers = 
    CompiledQuery.Compile(
        (DataContext dc)=>dc.Users.Select(x=>x)
    );
//        
Func<DataContext, string, IQueryable<User>> filterUserName = 
    CompiledQuery.Compile(
        (DataContext dc, string name) =>
            selectUsers(dc).Where(user=>user.Name == name)
    );

Calling and enumerating the chain works fine:

filterUserName(new DataContext(), "Otter").ToList();

Add a third query to the chain:

Func<DataContext, string, int, IQueryable<User>> filterUserAndGroup =     
    CompiledQuery.Compile(
        (DataContext dc, string name, int groupId) => 
            filterUserName(dc, name).Where(user=>user.GroupId == groupId)
    );

Calling the chain does not work:

filterUserAndGroup(new DataContext(), "Otter", 101);

System.InvalidOperationException:
Member access ‘String Name’ of ‘User’
not legal on type
‘System.Linq.IQueryable1[User].. at
System.Data.Linq.SqlClient.SqlMember.set_Expression(SqlExpression
value) at
System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression
expr, MemberInfo member) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.AccessMember(SqlMember
m, SqlExpression expo) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitMember(SqlMember
m) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitExpression(SqlExpression
expr) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitBinaryOperator(SqlBinary
bo) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitExpression(SqlExpression
expr) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitSelect(SqlSelect
select) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitAlias(SqlAlias
a) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlVisitor.VisitSource(SqlSource
source) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitSelect(SqlSelect
select) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlBinder.Visitor.VisitIncludeScope(SqlIncludeScope
scope) at
System.Data.Linq.SqlClient.SqlVisitor.Visit(SqlNode
node) at
System.Data.Linq.SqlClient.SqlBinder.Bind(SqlNode
node) at
System.Data.Linq.SqlClient.SqlProvider.BuildQuery(ResultShape
resultShape, Type resultType, SqlNode
node, ReadOnlyCollection1
parentParameters, SqlNodeAnnotations
annotations) at
System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression
query, SqlNodeAnnotations annotations)
at
System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Compile(Expression
query) at
System.Data.Linq.CompiledQuery.ExecuteQuery(DataContext
context, Object[] args) at
System.Data.Linq.CompiledQuery.Invoke(TArg0
arg0, TArg1 arg1) at TestMethod() in
….

Answer 1

Looks like you need to convert your first compiled query to a list before executing the second one. In theory that should have caused an error with your two queried chain as well.

From MSDN CompiledQuery:

If a new query operator is applied to the result of the delegate execution, an exception is generated.

When you want to execute a query operator over the result of executing a compiled query, you must translate the result to a list before operating on it.

Perhaps this code will fix it although that could have implications for the roundtrips back to the database if you’re using LINQ to SQL.

filterUserName(dc, name).ToList().Where(user=>user.GroupId == groupId)