Converting query expression to Linq method syntax

Question

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:

How to rewrite it?
What is the appropriate name for my query syntax and the new with Linq and Lambda (query expression and Linq to Entities???). Please give me a hit on this point I'm confused.

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

Thanks guys for your help on this!

Do you have a reason for the rewrite? Or is it just for learning more about LINQ? — svick
– svick, Commented Sep 29, 2011 at 11:14
svick I would like learn more about LINQ, at the moment my code is working. — GibboK
– GibboK, Commented Sep 29, 2011 at 11:21
The official names seem to be query syntax and method syntax. — svick
– svick, Commented Sep 29, 2011 at 11:52

Ladislav Mrnka · Accepted Answer · 2011-09-29 11:46:29Z

3

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.

answered Sep 29, 2011 at 11:46

Ladislav Mrnka

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3 Comments

GibboK Over a year ago

Thanks Ladislav for your explanation!

GibboK Over a year ago

So with LINQ-To-Entities means I can retrive the data working with the MODEL (so Navigational properties and so on).. correct? thnks

Ladislav Mrnka Over a year ago

LINQ-to-Entities means that you are querying entity model and LINQ provider is converting your queries to SQL.

mnsr · Accepted Answer · 2011-09-29 11:46:13Z

0

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.

answered Sep 29, 2011 at 11:46

mnsr

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Comments

usman tahir · Accepted Answer · 2019-04-11 11:47:29Z

0

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 });

answered Apr 11, 2019 at 11:47

usman tahir

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