Is it possible to link multiple compiled linq queries together?

Question

I am trying to combine several compiled linq queries together. I managed to combine the two queries together, but I cannot get the chain of three to work correctly. So, here is a shorthand for my code to recreate the problem. My two questions are: "Why is this not working?" and "Is there a better way to preserve the performance benefits of compiled queries and also avoid duplicating the main 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 a 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)
    );

Chaining does not work:

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

System.InvalidOperationException: "String Name" "User" "System.Linq.IQueryable 1[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, ReadOnlyCollection 1 parentParameters, SqlNodeAnnotations ) System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression , SqlNodeAnnotations) System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Compile(Expression ) System.Data.Linq.CompiledQuery.ExecuteQuery(DataContext , [] args) System.Data.Linq.CompiledQuery.Invoke(TArg0 arg0, TArg1 arg1) TestMethod() ....

Answer 1

, . .

MSDN CompiledQuery:

, .

, .

, , , LINQ to SQL.

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

Answer 2

, CompiledQuery. - LINQ - :

var result = dbContext.Users.Where(user => user.id == id);
result = result.Where(user => user.GroupID == groupID);
result = result.Select(user => user.username);

for(String username in result){ 
   ; // do something
}

, , . , , , (, -).

Answer 3

Do you need to use the CompiledQuery class? Try it...

static Func<DataContext, IQueryable<User>> selectUsers =
  (dc) => dc.Users.Select(x => x);
//        
static Func<DataContext, string, IQueryable<User>> filterUserName =
    (DataContext dc, string name) =>
        selectUsers(dc).Where(user => user.Name == name);
//
static Func<DataContext, string, int, IQueryable<User>> filterUserAndGroup =
    (DataContext dc, string name, int groupId) =>
        filterUserName(dc, name).Where(u => u.GroupID == groupId);

... test code (I know that my DataContext is not LINQ2SQL here, but it is LINQ's pleasure and beauty) ...

In addition, I use this method for my own databases, so I know that they are embedded in separate queries that will be sent to the database. I even used regular instance methods that return IQueryable <> instead of Func <> delegates.

public class DataContext
{
    public static Func<DataContext, IQueryable<User>> selectUsers =
      (dc) => dc.Users.Select(x => x);
    //        
    public static Func<DataContext, string, IQueryable<User>> filterUserName =
        (DataContext dc, string name) =>
            selectUsers(dc).Where(user => user.Name == name);
    //
    public static Func<DataContext, string, int, IQueryable<User>> UsrAndGrp =
        (DataContext dc, string name, int groupId) =>
            filterUserName(dc, name).Where(u => u.GroupID == groupId);

    public DataContext()
    {
        Users = new List<User>()
        {
            new User(){ Name = "Matt", GroupID = 1},
            new User(){ Name = "Matt", GroupID = 2},
            new User(){ Name = "Jim", GroupID = 2},
            new User(){ Name = "Greg", GroupID = 2}
        }.AsQueryable();
    }
    public IQueryable<User> Users { get; set; }
    public class User
    {
        public string Name { get; set; }
        public int GroupID { get; set; }
    }
}

class Program
{
    static void Main(string[] args)
    {
        var q1 = DataContext.UsrAndGrp(new DataContext(), "Matt", 1);
        Console.WriteLine(q1.Count()); // 1
        var q2 = DataContext.filterUserName(new DataContext(), "Matt");
        Console.WriteLine(q2.Count()); // 2
    }
}