Execute String as a Linq

Question

Is there a way I can execute a String as a Linq? I had a dynamci query and for that I had to convert the Linq expression into string, then append string bulider which has some conditional query. So whole expression is now in string. How to execute this string now? Should I again convert this string to Linq? How to proceed?

 StringBuilder sb = new StringBuilder();
 if (InstId != String.Empty)
 {
     sb.Append("application.Id ==" + InstId);
 }
 if (BId != String.Empty)
 {
     sb.Append("&& application.BId ==" + BId);
 }
 if (CId != String.Empty)
 {
     sb.Append("&& application.CId ==" + CId);
 }

String query=("from tables in context.Application .........
........join .........."+sb);

var q1=query;

Now how to execute this q1?

Answer 1

You don't need StringBuilder for that:

var query = context.Application;

if (InstId != String.Empty)
{
    query = query.Where(a => a.Id == InstId);
}
if (BId != String.Empty)
{
    query = query.Where(a => a.BId == BId);
}
if (CId != String.Empty)
{
    query = query.Where(a => a.CId == CId);
}

var items = query.Join(/* your join here */).ToList();

Query won't be executed untill ToList or other methods like that is invoked, so you can append Where() as long you'd like to.

Answer 2

While I don't necessarily think it's a great practice in a lot of cases, there is a Dynamic LINQ library that allows you to do just that.

In general, if possible, I'd recommend using something that can be more strongly type checked, such as @MarcinJuraszak's response or something like a PredicateBuilder class.