C# linq lambda join and select syntax

Question

I'm looking for the counterpart of Msql query:

SELECT per.*,add.addressDescription FROM Persons per 
       JOIN Address add ON per.AddressId = add.AddressId

I have this query:

    var query = persons.JOIN(address,per = person.addressId,add = addressId
    (per,add) => 
    new Persons{
                addressDescription = add.addressDescription,
                PersonId = per.PersonId,
                PersonFirstName = per.PersonFirstName
                PersonLastName = per.PersonLastName})

Is there a way to populate Persons.addressDescription without assigning individually the other properties of Persons? Imagine if Persons have 10 more properties.

I would like to refrain from using loops like:

foreach(Person person in PersonList)
{
  foreach(Address address in AddressList)
  {
     if(person.addressId == address.addressId){
        person.addressDescription = address.addressDescription
     }
   }
}

Possible duplicate of [What is the syntax for an inner join in LINQ to SQL?](http://stackoverflow.com/questions/37324/what-is-the-syntax-for-an-inner-join-in-linq-to-sql) — shA.t, Jul 11 '16 at 07:29
@shA.t hi and thanks for your reply, the problem is their question only asks how to return the Persons without populating Persons.AddressDescription. — user3770093, Jul 11 '16 at 07:37

score 3 · Answer 1 · answered Jul 11 '16 at 06:57

var id = 1;
var query = database.Posts    // your starting point - table in the "from" statement
   .Join(database.Post_Metas, // the source table of the inner join
      post => post.ID,        // Select the primary key (the first part of the "on" clause in an sql "join" statement)
      meta => meta.Post_ID,   // Select the foreign key (the second part of the "on" clause)
      (post, meta) => new { Post = post, Meta = meta }) // selection
   .Where(postAndMeta => postAndMeta.Post.ID == id);    // where statement

thanks for your reply but I think I will still need to loop it following your example. — user3770093, Jul 11 '16 at 07:02

Gilad Green · Accepted Answer · 2016-07-11T07:35:14.327

3

var query = persons.join(address,
    per = person.addressId,
    add = addressId
    (per,add) => 
    {
        per.addressDescription = add.addressDescription;
        return per;
    });

edited Jul 11 '16 at 07:35

answered Jul 11 '16 at 07:01

Gilad Green

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wow really, thats the first time I saw a return in the select statement. I'll give it a go now. – user3770093 Jul 11 '16 at 07:05
I can't use return function inside the query =/ – user3770093 Jul 11 '16 at 07:18
@user3770093 Show what you did because for me it works – Gilad Green Jul 11 '16 at 07:18
Hi mate thanks your solution worked! I had simple typo errors. Thank you so much! – user3770093 Jul 11 '16 at 07:57

C# linq lambda join and select syntax

2 Answers2