CODEWITHSUNDEEP
linqentity-frameworklinq-to-entities
GibboK
GibboK

Reputation: 73898

Converting query expression to Linq method syntax

I use EF 4 and C#.

I have a query like:

var contentsAuthor = from c in context.CmsContents
                     join a in context.CmsAuthors on c.AuthorId equals a.AuthorId
                     where a.UserId == userGuid
                     select new
                     {
                         c.Title,
                         c.ContentId
                     };

I would like rewrite it in Linq with Lambda Expression. My questions:

Notes: probably the title for this question is not appropriate, let me know I will improve it

Thanks guys for your help on this!

Upvotes: 1

Views: 1307

Answers (3)

usman tahir
usman tahir

Reputation: 301

var result = context.CmsContents
                        .Join(context.CmsAuthors.Where(x => x.auth.UserId == userGuid),
                         content => content.AuthorId,
                         author => author.AuthorId,
                         (cont, auth) => new { cont, auth })
                        .Select(x => new { x.cont.Title, x.cont.ContentId });

Upvotes: 0

Ladislav Mrnka
Ladislav Mrnka

Reputation: 364249

The lambda expression should look like:

var contentsAuthor = context.CmsContents
                            .Join(context.CmsAuthors, 
                                  content => content.AuthorId,
                                  author => author.AuthorId,
                                  (content,  author) => new { content, author })
                            .Where(x => x.author.UserId == userGuid)
                            .Select(x => new { x.content.Title, x.content.ContentId });

Both yours and this version are LINQ queries. This one uses lambdas directly whereas your version uses syntactic sugar available in C#. They are the same. LINQ-to-Entities have nothing to do with this.

Anyway if you are using LINQ-to-Entities your CmsContent should have Author property and your query would reduce to:

var contentsAuthor = context.CmsContents
                            .Where(c => c.Author.UserId == userGuid)
                            .Select(c => new { c.Title, c.ContentId });

The LINQ-to-Entities provider will make join for you when translating expression tree to SQL query.

Upvotes: 3

mnsr
mnsr

Reputation: 12437

Lambda:

var contentsAuthor = context.CmsContents
    .Join(context.CmsAuthors, c => c.AuthorId, a => a.AuthorId, (c, a) => new { Contents = c, Author = a })
    .Where(w => w.Author.UserId == userGuid)
    .Select(s => new { s.Contents.Title, s.Contents.ContentId });

The way you did it is fine though. I call it query syntax, but I'm not sure if it has an official name.

For this sort of stuff, check out LINQPad. In "Expression" mode, you can type a query like you have, and click on the Lambda symbol and it'll show you the lambda version of your query.

Upvotes: 0

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