How to do a join in linq to sql with method syntax

Question

I have seen lots of examples in LINQ to SQL examples on how to do a join in query syntax but I am wondering how to do it with method syntax  For example how might I do the following  var result   from sc in enumerableOfSomeClass              join soc in enumerableOfSomeOtherClass              on sc Property1 equals soc Property2              select new   SomeClass   sc  SomeOtherClass   soc     with a  Join    Can anyone illustrate or provide another simple example

User · Accepted Answer

var result   from sc in enumerableOfSomeClass              join soc in enumerableOfSomeOtherClass              on sc Property1 equals soc Property2              select new   SomeClass   sc  SomeOtherClass   soc      Would be equivalent to   var result   enumerableOfSomeClass      Join enumerableOfSomeOtherClass            sc   gt  sc Property1            soc   gt  soc Property2             sc  soc    gt  new                                                     SomeClass   sc                             SomeOtherClass   soc                              As you can see  when it comes to joins  query syntax is usually much more readable than lambda syntax

User · Answer

Justin has correctly shown the expansion in the case where the join is just followed by a select  If you ve got something else  it becomes more tricky due to transparent identifiers - the mechanism the C  compiler uses to propagate the scope of both halves of the join   So to change Justin s example slightly   var result   from sc in enumerableOfSomeClass              join soc in enumerableOfSomeOtherClass              on sc Property1 equals soc Property2              where sc X   sc Y    10              select new   SomeClass   sc  SomeOtherClass   soc     would be converted into something like this   var result   enumerableOfSomeClass      Join enumerableOfSomeOtherClass            sc   gt  sc Property1            soc   gt  soc Property2             sc  soc    gt  new   sc  soc         Where z   gt  z sc X   z sc Y    10       Select z   gt  new   SomeClass   z sc  SomeOtherClass   z soc       The z here is the transparent identifier - but because it s transparent  you can t see it in the original query

User · Answer

To add on to the other answers here  if you would like to create a new object of a third different type with a where clause  e g  one that is not your Entity Framework object  you can do this   public IEnumerable lt ThirdNonEntityClass gt  demoMethod IEnumerable lt int gt  property1Values        using var entityFrameworkObjectContext   new EntityFrameworkObjectContext                 var result   entityFrameworkObjectContext SomeClass              Join entityFrameworkObjectContext SomeOtherClass                  sc   gt  sc property1                  soc   gt  soc property2                   sc  soc    gt  new  sc  soc                Where s   gt  propertyValues Any pvals   gt  pvals    es sc property1               Select s   gt  new ThirdNonEntityClass                                dataValue1   s sc dataValueA                  dataValue2   s soc dataValueB                             ToList               return result           Pay special attention to the intermediate object that is created in the Where and Select clauses   Note that here we also look for any joined objects that have a property1 that matches one of the ones in the input list    I know this is a bit more complex than what the original asker was looking for  but hopefully it will help someone

[linq-to-sql] How to do a join in linq to sql with method syntax?

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