CODEWITHSUNDEEP
c#linq
Samuel Jenks
Samuel Jenks

Reputation: 1172

Is union available in LINQ query syntax?

I noticed that I was unable to structure a linq query with a union of two selects, using ANSI syntax.

The .net documentation has an article on query syntax examples where union is not shown. However, under .net examples for method syntax, a union example is given.

I know I can combine query syntax selects and Method based selects to bypass this problem, but I am curious if I can do entirely without method based syntax.

var strings =
          from MemberInfo member in Whitelist.Members
          select member.ToString()
          union
          from Type type in Whitelist.Types
          select type.ToString();

Upvotes: 10

Views: 12322

Answers (3)

Enigmativity
Enigmativity

Reputation: 117037

LINQ and ANSI queries only have passing similarities. There should be very little expectation that any of the ANSI syntax crosses over to LINQ.

UNION is no exception.

Here are my three preferred options:

(1)

var strings =
    Enumerable
        .Union(
            from MemberInfo member in Whitelist.Members
            select member.ToString(),
            from Type type in Whitelist.Types
            select type.ToString());

(2)

var members =
    from MemberInfo member in Whitelist.Members
    select member.ToString();

var types =
    from Type type in Whitelist.Types
    select type.ToString()

var strings = Enumerable.Union(members, types);

(3)

var strings =
    (
            from MemberInfo member in Whitelist.Members
            select member.ToString()
    ).Union(
            from Type type in Whitelist.Types
            select type.ToString()
    );

I like these options as they help to clearly show that a Union is being performed.

Upvotes: 5

TheGeneral
TheGeneral

Reputation: 81493

The answer is no. As much as you can do in query syntax, it lacks some basic operations (as you have seen). You will have to use the extension methods.

Given

Query Keywords (C# Reference)

Enumerable.Union Method (IEnumerable, IEnumerable)

Produces the set union of two sequences by using the default equality comparer.

Example

ProductA[] store1 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "orange", Code = 4 } };

ProductA[] store2 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "lemon", Code = 12 } };

var union = store1.Union(store2);

or

var union =
     (from MemberInfo member in Whitelist.Members select member.ToString()).Union
     (from Type type in Whitelist.Types select type.ToString());

or equivalent

var union =
    (from MemberInfo member in Whitelist.Members select member.ToString()).Concat
    (from Type type in Whitelist.Types select type.ToString()).Distinct();

Upvotes: 8

Leandro Sousa
Leandro Sousa

Reputation: 42

You need to use Union method. Like that.

var strings = (from MemberInfo member in Whitelist.Members
          select member.ToString())
          .Union(
          from Type type in Whitelist.Types
          select type.ToString());

Upvotes: 1

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