Constructing dynamic LINQ expressions is a pretty niche requirement, however, if you’re in the market for it you will likely want to extend some its expressions to fit your needs. Below I will demonstrate how to extend Microsoft’s .NET 4.0 implementation of System.Linq.Dynamic.
The first step is to create a class and replace it with the following:
using System;using System.Collections.Generic;using System.Linq;using System.Linq.Expressions;using System.Web;namespace System.Linq.Dynamic{ public static class DynamicQueryable { }}
Next we are going to implement a FirstOrDefault() extension. Add the following to your new class:
public static object FirstOrDefault(this IQueryable source) { if (source == null) throw new ArgumentNullException("source"); return source.Provider.Execute( Expression.Call( typeof(Queryable), "FirstOrDefault ", new Type[] { source.ElementType }, source.Expression)); }
Now you can implement it on your IQueryable to return a single dynamic object.
//In this case context is the DBContext and sqlQuery is a string builder that built our dynamic selectvar results = context.Set<YourEntityName>() .Where(a => a.Something == "Something") .Select(sqlQuery.ToString());var item = results.FirstOrDefault();We can do something similar to convert our Queryable to a List<dynamic> or IEnumerable<dynamic> in order to actually execute our dynamic query and bring it into memory:
public static IEnumerable<dynamic> AsEnumerable(this IQueryable source) { if (source == null) throw new ArgumentNullException("source"); foreach (var item in source) { yield return item; } }public static List<dynamic> ToDynamicList(this IQueryable source) { if (source == null) throw new ArgumentNullException("source"); var items = new List<dynamic>(); foreach (var item in source) { items.Add(item); } return items; }These extension methods, along with others you can implement, make working with dynamic linq much easier and more inline with what most of us are comfortable working with. Enjoy.
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