How to dynamic add filters to a LINQ query against an Odata Source in C#
c#, linq, odata, wcf-data-services
Solution
Following some other links , i found a couple of options. One would be to dynamically create the expression tree which became a quagmire rather quickly, the other is to build the $filter manually. However and add it with .AddQueryOption() . However if there are already other where clauses in the query this breaks since the resulting URL now has two $filter entries.. So what i do is take my original query, and then grab the URL and the querystring and grab the $filter , and then if it exists add my own dynamic stuff and run a new query. here is a demo (running in linqpad)
//Grab original query as a DataServiceQuery
DataServiceQuery<NetworkDevice> originalquery = (DataServiceQuery<NetworkDevice>)
(from x in NetworkDevices
where
x.Type == "switch"
select x);
//Get the HTTP QueryString
var querystr = (originalquery).RequestUri.Query;
var filter = System.Web.HttpUtility.ParseQueryString(querystr)["$filter"];
/* Create our own dynamic filter equivilant to
x.Name == "x" ||
x.Name == "y"
*/
string[] names = { "device1", "device2" };
StringBuilder sb = new StringBuilder();
sb.Append("(");
foreach (string s in names)
{
sb.Append(String.Format("Name eq '{0}'",s));
sb.Append(" or ");
}
sb.Remove(sb.Length - 4, 4);
sb.Append(")");
var dynamicfilter = sb.ToString();
// If there was an original filter we'll add the dynamic one with AND , otherwise we'll just use the dynamicone
var newfilter = dynamicfilter;
if ( filter != null && filter.Trim() != string.Empty )
{
newfilter = filter + " and " + newfilter;
}
newfilter.Dump();
var finalquery =
(from x in NetworkDevices.AddQueryOption("$filter",newfilter)
select x).Take(50);
finalquery.Dump();
Problem
I have a query like the following ``` var query = (from x in NetworkDevices where x.Name == "blabla1" || x.Name == "blabla2" select x ); ``` and i'm running it against an Odata endpoint, so it effectively gets translated into the following URL ``` https://targetserver/endpoint.svc/NetworkDevices()?$filter=Name eq 'blabla1' or Name eq 'blabla2' ``` So i want to dynamically add lots of those where filters... In C# i can just keep adding it to my query, but that isn't dynamic. I want to do it at runtime. If i was calling this from Javascript, well i can easily just update the URL as well. My Question, is in C# how do i dynamically add these filters to the where clause. in plain old LINQ (like linq 2 objects) i could do something like this. ``` var machines = new string[] { "blabla1" , "blabla2" } ; res1.Where ( x => machines.Contains(x.Name) ).ToArray() ``` and that would work, but that doesn't work against the Odata Endpoint as i get an error like this. The method 'Contains' is not supported So i presume the only way would be to dynamically , edit the expression tree or something to add those filters. Does anybody know how to do that?