predicate not working in join lambda expression

Question

I have using PredicateBuilder class to dynamically creating Where clause in LINQ statements.

Following is my code which is When using predicate

var predicate = PredicateBuilder.True<tbl_login>();
predicate = predicate.And(x => x.DAT_LOGIN_TIME >= startDate && x.DAT_LOGIN_TIME <= endDate);`
var data = context.tbl_login.Join(context.tbl_user, x => x.LNG_USER_PRIMARY_ID, y => y.LNG_USER_PRIMARY_ID, (x, y) => new
{
    userID = x.LNG_USER_PRIMARY_ID,
    loginTime = x.DAT_LOGIN_TIME,
    ageGroup = y.INT_AGE_GROUP
}).Where(predicate)
  .Select(x => new 
    { 
      userID = x.userID, 
      ageGroup = x.ageGroup 
    }).Distinct().ToList();

It gives me compile time exception cannot convert from System.Linq.Expressions.Expression<System.Func<JoyRydeAnalysis.Data.tbl_login,bool>>' to System.Linq.Expressions.Expression<System.Func<AnonymousType#1,int,bool>

What i am missing?

score 2 · Accepted Answer · answered Sep 29 '15 at 11:28

Your predicate is a predicate for tbl_login. But here, you're projecting to an anonymous type:

(x, y) => new
{
    userID = x.LNG_USER_PRIMARY_ID,
    loginTime = x.DAT_LOGIN_TIME,
    ageGroup = y.INT_AGE_GROUP
}

That predicate can't be applied to that projection.

I suspect you may want to apply the predicate earlier instead though:

var data = context.tbl_login
                  .Where(predicate)
                  .Join(...)
                  .Select(...)
                  .Distinct()
                  .ToList();

Note that at this point, your Select will be redundant, as you can just change the projection in the Join call.

It's also note clear why you're using PredicateBuilder at all, to be honest. You're only joining PredicateBuilder.True with a single expression - so you can just use:

var data = context.tbl_login
                  .Where(x => x.DAT_LOGIN_TIME >= startDate && x.DAT_LOGIN_TIME <= endDate)
                  .Join(...)
                  .Select(...)
                  .Distinct()
                  .ToList();

predicate not working in join lambda expression

1 Answers1