Linq to SQL not querying memory - linq

Question

I am using Linq for SQL and have always thought that I was querying the results of a Query in memory. I have just looked at the database and it is showing many thousands of queries rather than 1 which is what I expected.
My approach has been to run a query and then use linq to search within the resultset.
IQueryable<mapping> fieldList = from mm in db.mappings
join mi in db.metaItems on mm.secondaryMetaItemId equals mi.metaItemId
join mo in db.metaObjects on mi.metaObjectId equals mo.metaObjectId
where mm.linkageId == 277
select mm;
for (int i=0;i<100;i++)
{
mapping thisVar = fieldList.FirstOrDefault(m => m.primaryItem == info.Name);
}
How can I stop Linq requerying everytime I access my resultset...
Thanks for your help!

Answer 1

When you write a LINQ query, the query doesn't get actually get executed until you perform an action that actually enumerates over it (deferred execution). Calling FirstOrDefault() is an example of one such method that enumerates over the result (the first result has to be found). You'll want to call a method or otherwise enumerate over the results once. That way when you want to refer to those results throughout your program, you do it on a stored copy.
The easiest way you can do that is to convert it to a list. That will put the results in memory as a list. You could then use that.
IQueryable<mapping> fieldList =
from mm in db.mappings
join mi in db.metaItems on mm.secondaryMetaItemId equals mi.metaItemId
join mo in db.metaObjects on mi.metaObjectId equals mo.metaObjectId
where mm.linkageId == 277
select mm;
// save it!
var result = fieldList.ToList(); // query is processed only once here
// do stuff with result
for (int i=0;i<100;i++)
{
// using the stored result
thisVar = result.FirstOrDefault(m => m.primaryItem == info.Name);
}

Answer 2

try this :
var fieldList = (from mm in db.mappings
join mi in db.metaItems on mm.secondaryMetaItemId equals mi.metaItemId
join mo in db.metaObjects on mi.metaObjectId equals mo.metaObjectId
where mm.linkageId == 277
select mm).AsEnumerable();
foreach (int i=0;i<100;i++)
{
mapping thisVar = fieldList.FirstOrDefault(m => m.primaryItem == info.Name);
}