add singleOrDefault expression tree builder

Author: jaredcnance

JsonApiDotNetCore/Data/GenericDataAccess.cs

@@ -1,16 +1,42 @@
+using System;
+using System.Reflection;
 using System.Linq;
+using System.Linq.Expressions;
 using JsonApiDotNetCore.Extensions;
 using Microsoft.EntityFrameworkCore;
 
-public class GenericDataAccess
+namespace JsonApiDotNetCore.Data
 {
-  public DbSet<T> GetDbSet<T>(DbContext context) where T : class
+  public class GenericDataAccess
   {
-    return context.Set<T>();
-  }
+    public DbSet<T> GetDbSet<T>(DbContext context) where T : class
+    {
+      return context.Set<T>();
+    }
 
-  public IQueryable<T> IncludeEntity<T>(IQueryable<T> queryable, string includedEntityName) where T : class
-  {
-    return queryable.Include(includedEntityName);
+    public IQueryable<T> IncludeEntity<T>(IQueryable<T> queryable, string includedEntityName) where T : class
+    {
+      return queryable.Include(includedEntityName);
+    }
+
+    public T SingleOrDefault<T>(object query, string param, string value)
+    {
+      var queryable = (IQueryable<T>) query;
+      var currentType = queryable.ElementType;
+      var property = currentType.GetProperty(param);
+
+      if (property == null)
+      {
+        throw new ArgumentException($"'{param}' is not a valid property of '{currentType}'");
+      }
+
+      var prm = Expression.Parameter(currentType, property.Name);
+      var left = Expression.Convert(Expression.PropertyOrField(prm, property.Name), typeof(string));
+      var right = Expression.Constant(1, property.PropertyType);
+      var body = Expression.Equal(left, right);
+      var where = Expression.Lambda<Func<T, bool>>(body, prm);
+
+      return queryable.SingleOrDefault(where);
+    }
   }
 }

JsonApiDotNetCore/Data/ResourceRepository.cs

@@ -25,18 +25,14 @@ public List<object> Get()
 
     public object Get(string id)
     {
-      if (_context.Route is RelationalRoute)
-      {
-        return GetRelated(id, _context.Route as RelationalRoute);
-      }
-      return GetEntityById(_context.Route.BaseModelType, id, null);
+      var route = _context.Route as RelationalRoute;
+      return route != null ? GetRelated(id, route) : GetEntityById(_context.Route.BaseModelType, id, null);
     }
 
     private object GetRelated(string id, RelationalRoute relationalRoute)
     {
-      // HACK: this would rely on lazy loading to work...will probably fail
       var entity = GetEntityById(relationalRoute.BaseModelType, id, relationalRoute.RelationshipName);
-      return relationalRoute.BaseModelType.GetProperties().FirstOrDefault(pi => pi.Name.ToCamelCase() == relationalRoute.RelationshipName.ToCamelCase()).GetValue(entity);
+      return relationalRoute.BaseModelType.GetProperties().FirstOrDefault(pi => pi.Name.ToCamelCase() == relationalRoute.RelationshipName.ToCamelCase())?.GetValue(entity);
     }
 
     private IQueryable GetDbSetFromContext(string propName)
@@ -47,21 +43,26 @@ private IQueryable GetDbSetFromContext(string propName)
 
     private object GetEntityById(Type modelType, string id, string includedRelationship)
     {
-      // HACK: I _believe_ by casting to IEnumerable, we are loading all records into memory, if so... find a better way...
-      //        Also, we are making a BIG assumption that the resource has an attribute Id and not ResourceId which is allowed by EF
+      // get generic dbSet
       var dataAccessorInstance = Activator.CreateInstance(typeof(GenericDataAccess));
-      var dataAccessorMethod = dataAccessorInstance.GetType().GetMethod("GetDbSet");
-      var genericMethod = dataAccessorMethod.MakeGenericMethod(modelType);
-      var dbSet = genericMethod.Invoke(dataAccessorInstance, new [] {((DbContext) _context.DbContext) });
+      var dataAccessorGetDbSetMethod = dataAccessorInstance.GetType().GetMethod("GetDbSet");
+      var genericGetDbSetMethod = dataAccessorGetDbSetMethod.MakeGenericMethod(modelType);
+      var dbSet = genericGetDbSetMethod.Invoke(dataAccessorInstance, new [] {((DbContext) _context.DbContext) });
 
+      // include relationships if requested
       if (!string.IsNullOrEmpty(includedRelationship))
       {
         var includeMethod =  dataAccessorInstance.GetType().GetMethod("IncludeEntity");
         var genericIncludeMethod = includeMethod.MakeGenericMethod(modelType);
         dbSet = genericIncludeMethod.Invoke(dataAccessorInstance, new []{ dbSet, includedRelationship.ToProperCase() });
       }
 
-      return (dbSet as IEnumerable<dynamic>).SingleOrDefault(x => x.Id.ToString() == id);
+      // get the SingleOrDefault value by Id
+      var dataAccessorSingleOrDefaultMethod = dataAccessorInstance.GetType().GetMethod("SingleOrDefault");
+      var genericSingleOrDefaultMethod = dataAccessorSingleOrDefaultMethod.MakeGenericMethod(modelType);
+      var entity = genericSingleOrDefaultMethod.Invoke(dataAccessorInstance, new[] { dbSet, "Id", id });
+
+      return entity;
     }
 
     public void Add(object entity)