convert this LINQ expression into Lambda

Question

Guys, I have a hard time converting this below linq expression(left join implementation) to lambda expression (for learning).

var result = from g in grocery
       join f in fruit on g.fruitId equals f.fruitId into tempFruit
       join v in veggie on g.vegid equals v.vegid into tempVegg
       from joinedFruit in tempFruit.DefaultIfEmpty()
       from joinedVegg in tempVegg.DefaultIfEmpty()
       select new { g.fruitId, g.vegid, fname = ((joinedFruit == null) ? string.Empty :     joinedFruit.fname), vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) };

Can some one suggest me how to do this.

And i really appreciate if someone give me the excellent tutorial links for "C# Lambdas & Linqs"

Solution 1

To convert a Linq query to it's Lambda equivalent:

1. Download Linqpad and run your query.
2. In the results window, click on the "λ" button in the toolbar. It's right above the Results window
3. Your query will be converted to a Lambda expression equivalent!

Solution 2

You can take a look at 101 LINQ Samples and C# 3.0 QUERY EXPRESSION TRANSLATION CHEAT SHEET

Solution 3

Here's the heuristic that I follow:

Favor LINQ expressions over lambdas when you have joins.

I think that lambdas with joins look messy and are difficult to read.

Solution 4

I usually use ReSharper to help me convert things to method chains and lambda's, which helps me go back and forth fairly easy.

    var result = from g in grocery
                 join f in fruit on g.fruitId equals f.fruitId into tempFruit
                 join v in veggie on g.vegid equals v.vegid into tempVegg
                 from joinedFruit in tempFruit.DefaultIfEmpty()
                 from joinedVegg in tempVegg.DefaultIfEmpty()
                 select new { g.fruitId, g.vegid, fname = ((joinedFruit == null) ? string.Empty : joinedFruit.fname), vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) };

And then using ReSharper's option of convert LINQ to method chain equals the following:

        var result =grocery .GroupJoin(fruit, g => g.fruitId, f => f.fruitId, (g, tempFruit) => new {g, tempFruit})
                            .GroupJoin(veggie, @t => @t.g.vegid, v => v.vegid, (@t, tempVegg) => new {@t, tempVegg})
                            .SelectMany(@t => @[email protected](), (@t, joinedFruit) => new {@t, joinedFruit})
                            .SelectMany(@t => @[email protected](),(@t, joinedVegg) =>
                                new
                                    {
                                        @t.@[email protected],
                                        @t.@[email protected],
                                        fname = ((@t.joinedFruit == null) ? string.Empty : @t.joinedFruit.fname),
                                        vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname)
                                    });

Granted the output is less then desirable, but It at least helps in starting somewhere on understanding the syntax.

Solution 5

Here’s how you might write this query in lambda:

var cus­tomers = new List {
new Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1” },
new Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2” },
};

var user­Cus­tomers = new List {
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “not-admin”     },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “not-admin” },
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “admin” }
};

Using query expres­sion

var query =
from c in cus­tomers
join uc in user­Cus­tomers on
new { c.CompanyId, c.CustomerId } equals new { uc.CompanyId, uc.CustomerId }
where c.CompanyId == “AC” && uc.User == “admin“
select c;

Using lambda expres­sions

var lambda =  cus­tomers.Where(c => c.CompanyId == “AC”) // inner sequence
.Join(userCustomers.Where(uc => uc.User == “admin”), // outer sequence
c => new { c.CompanyId, c.CustomerId }, // inner key selec­tor
uc => new { uc.CompanyId, uc.CustomerId }, // outer key selec­tor
(c, uc) => c);

Both approach yields the same result (cus­tomer with com­pany Id “AC” and cus­tomer Id “Customer1”), but as you can see, lambda expres­sion is much harder to write and read!

Hope this helps!

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Comments

[RameshVel]

thanks jim for the reply. But i wanted to do this in lambda to get familiar with.. i mentioned that already its for learning...

[RameshVel]

thanks for the links Dzmitry... the cheat sheet is useful... i already have a look at 101 samples..

[satyavrat]

i thought that was only the paid version that had loads of samples etc

[Mitch Wheat]

The free version comes with samples too.

[RameshVel]

hey where would i get the source code for the 101 samples.. any idea.. i couldnt find there...

[RameshVel]

thanks Mark for your response.. i will run it over here and will let you know if that works..

[atconway]

I have Linqpad but without creating a 'connection' to a service that I can query, I can not see the button for the lambda. I do not know how to just paste in a LINQ query and convert it to a lambda. Is this actually possible?

[Brad Parks]

I just added a pic for where the button is in the UI. I don't have Linqpad on hand, but I think you need to have a runnable query there before it can be converted to a Lambda. In another post, I detailed how you can test data in Linqpad without needing a DB, here: stackoverflow.com/questions/4611031/…

[Toolkit]

can it convert SQL to lambda or LINQ? Doesn't seem to be working

[Brad Parks]

I haven't used it in a long time, but what does clicking the SQL button beside the λ do?