Question
linq to entities is what I'm using (EF). My constructor accepts four string arguments. I have to generate the linq query based on which parameter is not null. I can use if-else clauses, but I also have another constructor with ten arguments, so there will be a lot of different combinations to test.
Example:
Constructor(p1,p2,p3,p4)
{
var prod= from p in ctxt.products.expand("items\details")
where p.x==p1 && p.xx==p2 && p.xxx==p3 && p.xxxx==p4
select p;
}
Only if the argument is not null should there be condition tests in the where clause mentioned above. Specifically, the where clause should be as follows if p2 is null:
where p.x==p1 && p.xxx==p3 && p.xxxx==p4
Upon p2 and p3 becoming null,
where p.x==p1 && p.xxxx==p4
Can someone please advise me on how to proceed? If at all feasible, could you provide some example code?
Accepted Answer
DeferredExecution in Linq to the rescue. The execution of a Linq query depends on the request for data.
var prod = from p in ctxt.products.expand("items\details")
select p;
if (p1 != null)
{
prod = prod.Where(p => p.x == p1);
}
if (p2 != null)
{
prod = prod.Where(p => p.xx == p2);
}
// Execute the query
var prodResult = prod.ToList();
Popular Answer
There's always the option to compose the query piecemeal and benefit from delayed query execution:
public Constructor(int? p1, int? p2, int? p3, int? p4)
{
var prod = ctxt.products.expand("items\details");
if(p1 != null)
prod = prod.Where(p.x == p1);
if(p2 != null)
prod = prod.Where(p.xx == p2);
if(p3 != null)
prod = prod.Where(p.xxx == p3);
if(p4 != null)
prod = prod.Where(p.xxxx == p4);
}
Related Questions
Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
