Dynamic where clause in Linq to Entities

Question

Dynamic where clause in Linq to Entities

dynamic entity-framework linq where-clause

Question

I'm using linq to entities(EF). I have a constructor which takes 4 string parameters. Depending on what parameter is not null I have to build the linq query. I can do with if else statements but i also has other constructor with 10 parameters in that case there will be many combinations to check.

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;
}

In the above where clause there should be condition checks only if the parameter is not null. ie., if p2 is null then the where clause should look like

where p.x==p1 && p.xxx==p3 && p.xxxx==p4

if p2 and p3 are null then

where p.x==p1 && p.xxxx==p4

Can anyone tell me how to handle this. if possible can you give sample code for this

Deepak

Popular Answer

You could always build the query in pieces and take advantage of 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);
}

Justin Niessner

View more on Stack Overflow

amit_g · Accepted Answer · 2/3/2012 12:48:09 AM

Linq's DeferredExecution to rescue. Linq query is not executed unless the data is requested from it.

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();

Dynamic where clause in Linq to Entities

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