EF deferred execution using SQLquery as input - entity-framework

Question

I am trying to get an entity with EF by having an initial sql as input.
I tried the context.Entities.SQLQuery method but this returns a DBSet when I require an IQueriable.
I learned that I cannot transform DBSet to IQueryable because the first is already a result of data while the second is the container for the results of a "query" (executed yet or not). Correct me if i'm wrong :)
So I thought that when I write the following lambda I get the resulting query:
db.MyTable.Where(x => x.id == "123")
Becomes:
SELECT * FROM myTable WHERE id = '123'
With this I thought if I can set directly my query without needing to set my lambda...
Is that an option?
Or an alternative?
Thanks!

Answer 1

It's a bit unclear what you mean:
I am trying to get an entity with EF having an initial sql as input.
I'd interpret this, as that you have an SQL statement as input of something and you want to get an entity framework entity that would have this statement (whatever having a statement means)? Not understandable!
I learned that I cannot transform DBSet to IQueryable because the
first (the DbSet) is already a result of data while the second (the IQueryable) is the container for the results of a "query"
NOT!
Every DbSet<T> implements IQueryable<T>, meaning that if you have an object of class DbSet<t>, this object implements all functionality of IQueryable<T>. Just using this IQueryable does not execute the query. The query will only be executed once the first element of the sequence if requested.
using (var dbContext = new MyDbcontext())
{
var result = dbContext.MyItems
.Where(item => ...)
.Select(item => new
{
X = item.Property1,
Y = item.Property2,
...
};
Until here, the first element of the sequence is not asked, the query is not performed yet. No communication with the database was needed (except to create the dbContext object)
Only if you use execution functions like ToList(),Count(), First(), Max(), etc, the query is performed.
You can check this, because you get exceptoin if you do these kind of functions after the using block:
Wrong
IQueryable largeItems;
using (var dbContext = new MyDbcontext())
{
largeItems = dbContext.MyItems
.Where(item => item.Size > 1000);
// query not executed yet
}
int nrOfLargeItems = largeItems.Count();
// exception, query executed after dbContext is disposed
correct
int nrOfLargeItems;
using (var dbContext = new MyDbcontext())
{
var largeItems = dbContext.MyItems
.Where(item => item.Size > 1000);
// query not executed yet
nrOfLargeItems = largeItems.Count();
// the query is performed
}
Conclusion: users of a DbSet<T> inside a dbContext can use the DbSet<T> as if it was an IQueryable<T>, the query will not be executed until you perform any function that needs the first element of the query.
This includes complex functions like Join, GroupBy, OrderBy, etc. You can recognize these functions because MSDN add the following to the remarks section
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach.