feat(*): add AttrFilterQuery

Author: jaredcnance

src/JsonApiDotNetCore/Extensions/IQueryableExtensions.cs

@@ -63,7 +63,7 @@ private static IOrderedQueryable<TSource> CallGenericOrderMethod<TSource>(IQuery
             return (IOrderedQueryable<TSource>)result;
         }
 
-        public static IQueryable<TSource> Filter<TSource>(this IQueryable<TSource> source, FilterQuery filterQuery)
+        public static IQueryable<TSource> Filter<TSource>(this IQueryable<TSource> source, AttrFilterQuery filterQuery)
         {
             if (filterQuery == null)
                 return source;

src/JsonApiDotNetCore/Internal/Query/AttrFilterQuery.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Linq;
+using JsonApiDotNetCore.Models;
+using JsonApiDotNetCore.Services;
+
+namespace JsonApiDotNetCore.Internal.Query
+{
+  public class AttrFilterQuery
+  {
+    private readonly IJsonApiContext _jsonApiContext;
+
+    public AttrFilterQuery(
+        IJsonApiContext jsonApiCopntext,
+        FilterQuery filterQuery)
+    {
+      _jsonApiContext = jsonApiCopntext;
+
+      var attribute = GetAttribute(filterQuery.Key);
+
+      if (attribute == null)
+        throw new JsonApiException("400", $"{filterQuery.Key} is not a valid property.");
+
+      FilteredAttribute = attribute;
+      PropertyValue = filterQuery.Value;
+      FilterOperation = GetFilterOperation(filterQuery.Operation);
+    }
+
+    public AttrAttribute FilteredAttribute { get; set; }
+    public string PropertyValue { get; set; }
+    public FilterOperations FilterOperation { get; set; }
+
+    private FilterOperations GetFilterOperation(string prefix)
+    {
+      if (prefix.Length == 0) return FilterOperations.eq;
+
+      FilterOperations opertion;
+      if (!Enum.TryParse<FilterOperations>(prefix, out opertion))
+        throw new JsonApiException("400", $"Invalid filter prefix '{prefix}'");
+
+      return opertion;
+    }
+
+    private AttrAttribute GetAttribute(string propertyName)
+    {
+      return _jsonApiContext.RequestEntity.Attributes
+          .FirstOrDefault(attr =>
+              attr.InternalAttributeName.ToLower() == propertyName.ToLower()
+      );
+    }
+  }
+}