While somewhat powerful, the System.Linq.Dynamic library has a surprising lack of documentation, especially in regards to what conventions must be followed for more complex queries.
In a query I'm working on, it contains a FirstOrDefault
call, but I can't seem to get it to work.
Here's the whole (unworking) expression:
"Locations.FirstOrDefault(x => x.IsPrimaryLocation).Address1 as Address"
Can I write this FirstOrDefault expression to work with Dynamic linq?
What is the correct way to write this expression?
Extending the dynamic library is certainly an option as already suggested.
an alternative given the Where
in Dynamic Linq returns an Iqueryable
public static class DynamicQueryable {
public static IQueryable<T> Where<T>(this IQueryable<T> source, string predicate, params object[] values) { return (IQueryable<T>) Where((IQueryable) source, predicate, values); }
public static IQueryable Where(this IQueryable source, string predicate, params object[] values) {
using a DYnamic Object for the context or repository "locations".
Then use a where which could contain dynamic string predicate and follow with firstOrDefault.
(catch or test for null not considered)
DynamicLocations.Where(x => x.IsPrimaryLocation).FirstOrDefault( ).Address1 as Address;
or dynamic where if needed
DynamicLocations.Where("IsPrimaryLocation",new string[]).FirstOrDefault( ).Address1 as Address;
Details: You can expose on a method on a generic repository Class which you instantiate as a dynamic
public virtual IQueryable<TPoco> DynamicWhere(string predicate, params object[] values) {
return AllQ().Where(predicate, values);
}
Dynamic Generic Repository instantiation Sample
public class RepositoryFactory<TPoco> where TPoco : BaseObject,new() {
public IRepositoryBase<TPoco> GetRepository(DbContext context) {
// get the Pocotype for generic repository instantiation
var pocoTypes = new[] {typeof (TPoco)}; // but supports <T,U>
Type repBaseType = typeof (RepositoryBase<>);
IRepositoryBase<TPoco> repository = InstantiateRepository(context, repBaseType, pocoTypes);
return repository;
}
private IRepositoryBase<TPoco> InstantiateRepository(DbContext context, Type repType, params Type[] args) {
Type repGenericType = repType.MakeGenericType(args);
object repInstance = Activator.CreateInstance(repGenericType, context);
return (IRepositoryBase<TPoco>)repInstance;
}
}