Convert linq query into lambda query with joins

Question

I am new to lambda. how can i write below code using lambda. thanks

User user1 = (from u in db.Users
                                  join h in db.HCM_SMS_ROLE_MAPPINGs
                                  on u.roleID equals h.SMS_Role_ID
                                  where (u.Employee_Code == employeeCode && u.isDeleted == false && h.Is_Active_App == true)
                                  select u).Distinct().FirstOrDefault();

I think you meant from query syntax to method syntax because both would be considered LINQ — Aarif
– Aarif, Commented Apr 4, 2019 at 8:02

Zeeshan Adil · Accepted Answer · 2019-04-04 08:01:03Z

2

This should work for you:

db.Users.Join(db.HCM_SMS_ROLE_MAPPINGs, u => u.roleID, h => h.SMS_Role_ID, (u, h) => new
{
u, h
}
).Where(x=> x.u.Employee_Code == employeeCode && x.u.isDeleted == false && x.h.Is_Active_App == true).Select(x=> x.u).Distinct().FirstOrDefault()

Clean and Simple! Hope it helps

answered Apr 4, 2019 at 8:01

Zeeshan Adil

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6 Comments

Mrinal Kamboj Over a year ago

that's the correct lambda version for the query syntax in the question, though please remember for Distinct to work on the complete object either pass IEqualityComparer or implement IEquatable

Zeeshan Adil Over a year ago

@MrinalKamboj can you please suggest an edit explaining that? I don't understand how to do it correctly.

Mrinal Kamboj Over a year ago

that's the overload of the Disntinct, which can be supplied an IEqualityComparer, or the class needs to implement IEquatable, so when class doesn't implement IEquatable, then we go for the external IEqualityComparer, these are points which helps in resolving issues in a class object doing the equality comparison else it goes for the reference comparison instead of the value / property comparison which we are generally expecting for the primitive types

Zeeshan Adil Over a year ago

@MrinalKamboj is it like I make a class inherit from IEqualityComparer of type ClassToBeCompared and add a method Equals to it? like this:

class Compare : IEqualityComparer<ClassToBeCompared>     { public bool Equals(ClassToBeCompared x, ClassToBeCompared y) {     return x.Numf == y.Numf; } }

Mrinal Kamboj Over a year ago

yes you can use IEqualityComparer derived class if the class doesn't implement IEquatable by default, idea is to do value comparison for the reference types, which might otherwise check the reference equality by default

|

er-sho · Accepted Answer · 2019-04-04 07:54:54Z

0

My method is to right click the lightbulb in the left hand side bar and select 'Convert LINQ to method chain', which gives this:

User user1 = (db.Users
                .Join(db.HCM_SMS_ROLE_MAPPINGs, 
                   u => u.roleID, 
                   h => h.SMS_Role_ID, 
                   (u, h) => new { u, h })
                .Where(@t => (u.Employee_Code == employeeCode && u.isDeleted == false && h.Is_Active_App == true))
                .Select(@t => u))
                .Distinct()
                .FirstOrDefault();

I think this is a Resharper feature.

edited Apr 4, 2019 at 7:54

er-sho

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answered Apr 4, 2019 at 7:50

Robin Bennett

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1 Comment

Mrinal Kamboj Over a year ago

great though you may add an explanation, not everyone would have the Resharper

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