I have a string that contains a linq query and i have a dynamic where clause also as string that contains many dynamic condition here is my where clause
string strWhereString = "where a.id==1 && a.name==\"something\"";
and here is my linq query string :
var query = "from a in context.tblName "+strWhereString;
the question is how to run this query and get result from the table? Is there any way to do that or Linq doesn't support this ?
What you're looking for is something like System.Linq.Dynamic
which will give you the possibility to translate a query like:
var query = from p in northwind.Products
where p.CategoryID == 3 && p.UnitPrice > 3
orderby p.SupplierID
select p;
into:
var query = northwind.Products
.Where("CategoryID = 3 AND UnitPrice > 3")
.OrderBy("SupplierID");
also here is a good starting point, which has a good blog post and some examples to download.
Maybe you'll have more luck using the linq static methods:
context.tblName.Where(a=>a.id==1 && a.name=="something")
This way is really easy to add where clauses (or other) dynamically:
context.tblName..Where(a=>a.id==1 && a.name=="something").Where(a=>otherClause(a))
I'm not sure if this is really what you're looking for, but I think this is the right direction.
I also had to deal with dynamic conditions for doing a DB search. Instead of string parsing or dynamic LINQ, I came up with this solution. errorsOnly, startDate and endDate can (but must not) be set in the frontend. Additional conditions can simply be added accordingly:
var query = from x in db.DoubleDataValueArchive select x;
query = query.Where(x => x.DataPointId != null);
// Check if only errors should be shown (that are listed in errorDps)
List<int> errorDps = new List<int>();
if (errorsOnly.HasValue) {
if (errorsOnly == true)
{
errorDps = db.DataPoints.Where(x => x.DataType == 4).Select(x => x.Id).ToList();
query = query.Where(x => errorDps.Contains((int)x.DataPointId));
}
}
// Start Date
if (startDate.HasValue) {
startDate = startDate.Value.ToUniversalTime();
query = query.Where(x => x.DateValue >= startDate);
}
// End Date
if (endDate.HasValue)
{
endDate = endDate.Value.ToUniversalTime();
query = query.Where(x => x.DateValue <= endDate);
}
...and so on. This is completely dynamic but safe to work with at the same time. The assembled SQL query only gets finally executed once, when you make a list or similar out of the IQueryable.
I think what you are looking for is Dynamic LINQ. This is a library provided by the LINQ team itself.
What you need to do is use string expressions instead as shown in this blog - http://weblogs.asp.net/scottgu/dynamic-linq-part-1-using-the-linq-dynamic-query-library
