linq to sql join

[Chris]

hi,
I have i.e a linq result:
var result = from c in context.c select c;

I want to write a second linq query joined with the result above:
var second = from d in context.d join ... <now, I want to join it with
result>.

is it possible?

 

[Peter Duniho]

hi,
I have i.e a linq result:
var result = from c in context.c select c;

I want to write a second linq query joined with the result above:
var second = from d in context.d join ... <now, I want to join it with
result>.

is it possible?

Sure.

Start here:
http://msdn.microsoft.com/en-us/library/bb397676.aspx

Also read here:
http://msdn.microsoft.com/en-us/library/bb310804.aspx

 

[Alberto Poblacion]

hi,
I have i.e a linq result:
var result = from c in context.c select c;

I want to write a second linq query joined with the result above:
var second = from d in context.d join ... <now, I want to join it with
result>.

is it possible?

Why do you want it in two separate queries? You could perform the join
directly when you write the first of the queries:

var result = from c in context.c
join d in context.d on c.field equals d.field
select new { c.something, d.something };

This will send the join to the database server where it will be resolved
efficiently. If you retrieve a resultset and then perform the join in a
second linq query, then the join will have to be performed in memory at the
client side, which will normally require transferring unnecesary records
from the server into the client.

 

[Chris]

ok, thank u very much for help.
Anyway, I have sql query:

select * from tab n
join
(
select a, b, c from tab
where a in (select x from tab2 where y=z)
)m
on n.a=m.a

I want to have this query in linq to sql. Can u help me? I have problems how
to write where in (<select>) clause and then join it.

 

[Alberto Poblacion]

Anyway, I have sql query:

select * from tab n
join
(
select a, b, c from tab
where a in (select x from tab2 where y=z)
)m
on n.a=m.a

I want to have this query in linq to sql. Can u help me? I have problems
how
to write where in (<select>) clause and then join it.

You dont't have subqueries in linq, so you will need to rewrite your code
as a join. If I am not mistaken, your query can be rewritten in some way
similar to the following (and if I am mistaken, just ask the question in one
of the Sql forums and someone will tell you how to refactor your query so
that the subclause is converted into a join):

select tab1.*, tab2.a, tab2.b, tab2.c from tab1
join tab2 on tab1.a=tab2.a
join tab3 on tab2.a=tab3.x
where tab3.y=z

Once your query is refactored in this way, you can easily express it in
LINQ:

var q = from v1 in cts.tab1
join v2 in ctx.tab2 on v1.a equals v2.a
join v3 in ctx.tab3 on v2.a equals v3.x
where v3.y==z
select new {v1, v2.a, v2.b, v2.c };

 

[Chris]

Ok, thank u.
One question abou linq query. I wrote:
join v2 in ctx.tab2 on v1.a equals v2.a

can u write:
join v2 in ctx.tab2 on v1.a = v2.a

(= instead of equals)?

 

[Alberto Poblacion]

Ok, thank u.
One question abou linq query. I wrote:
join v2 in ctx.tab2 on v1.a equals v2.a

can u write:
join v2 in ctx.tab2 on v1.a = v2.a

(= instead of equals)?

No, the "join" in LINQ requires the "equals" keyword. You use == in the
"where" clause (note the C-style "double equals" instead of the SQL-style
"single equals", since we are writng C# and not SQL).