Eager loading (#701)

* Added eager loading of one-to-one and one-to-many entity relations

* Removed dead code

* Fixed: Eagerloads can have nested Eagerload properties

* Added safeguard against infinite loop.

* Cleanup and realign of project files

* Removed unused project dependencies

* Empty commit to restart TravisCI

* Post-merge fixes

* Post-merge fixes

* More post-merge fixes

* Review feedback: make EagerLoad private

Author: Bart Koelman

benchmarks/Benchmarks.csproj

@@ -5,11 +5,11 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
-    <PackageReference Include="moq" Version="$(MoqVersion)" />
+    <ProjectReference Include="..\src\JsonApiDotNetCore\JsonApiDotNetCore.csproj" />
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\src\JsonApiDotNetCore\JsonApiDotNetCore.csproj" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
+    <PackageReference Include="Moq" Version="$(MoqVersion)" />
   </ItemGroup>
 </Project>

src/Examples/JsonApiDotNetCoreExample/Models/Country.cs

@@ -0,0 +1,8 @@
+namespace JsonApiDotNetCoreExample.Models
+{
+    public class Country
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+    }
+}

src/Examples/JsonApiDotNetCoreExample/Models/Passport.cs

@@ -1,13 +1,50 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
+using System.Linq;
 using JsonApiDotNetCore.Models;
 
 namespace JsonApiDotNetCoreExample.Models
 {
-    public sealed class Passport : Identifiable
+    public class Passport : Identifiable
     {
+        [Attr]
         public int? SocialSecurityNumber { get; set; }
+
+        [Attr]
         public bool IsLocked { get; set; }
 
         [HasOne]
         public Person Person { get; set; }
+
+        [Attr]
+        [NotMapped]
+        public string BirthCountryName
+        {
+            get => BirthCountry.Name;
+            set
+            {
+                if (BirthCountry == null)
+                {
+                    BirthCountry = new Country();
+                }
+                
+                BirthCountry.Name = value;
+            }
+        }
+
+        [EagerLoad]
+        public Country BirthCountry { get; set; }
+
+        [Attr(isImmutable: true)]
+        [NotMapped]
+        public string GrantedVisaCountries
+        {
+            get => GrantedVisas == null ? null : string.Join(", ", GrantedVisas.Select(v => v.TargetCountry.Name));
+            // The setter is required only for deserialization in unit tests.
+            set { }
+        }
+
+        [EagerLoad]
+        public ICollection<Visa> GrantedVisas { get; set; }
     }
 }

src/Examples/JsonApiDotNetCoreExample/Models/Visa.cs

@@ -0,0 +1,15 @@
+using System;
+using JsonApiDotNetCore.Models;
+
+namespace JsonApiDotNetCoreExample.Models
+{
+    public class Visa
+    {
+        public int Id { get; set; }
+
+        public DateTime ExpiresAt { get; set; }
+
+        [EagerLoad]
+        public Country TargetCountry { get; set; }
+    }
+}

src/Examples/ReportsExample/ReportsExample.csproj

@@ -8,7 +8,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Dapper" Version="2.0.30" />
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="$(NpgsqlPostgreSQLVersion)" />
   </ItemGroup>
 </Project>

src/JsonApiDotNetCore/Builders/ResourceGraphBuilder.cs

@@ -79,10 +79,10 @@ public IResourceGraphBuilder AddResource(Type resourceType, Type idType = null,
             IdentityType = idType,
             Attributes = GetAttributes(entityType),
             Relationships = GetRelationships(entityType),
+            EagerLoads = GetEagerLoads(entityType),
             ResourceDefinitionType = GetResourceDefinitionType(entityType)
         };
 
-
         protected virtual List<AttrAttribute> GetAttributes(Type entityType)
         {
             var attributes = new List<AttrAttribute>();
@@ -179,6 +179,39 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
         protected virtual Type GetRelationshipType(RelationshipAttribute relation, PropertyInfo prop) =>
             relation.IsHasMany ? prop.PropertyType.GetGenericArguments()[0] : prop.PropertyType;
 
+        private List<EagerLoadAttribute> GetEagerLoads(Type entityType, int recursionDepth = 0)
+        {
+            if (recursionDepth >= 500)
+            {
+                throw new InvalidOperationException("Infinite recursion detected in eager-load chain.");
+            }
+
+            var attributes = new List<EagerLoadAttribute>();
+            var properties = entityType.GetProperties();
+
+            foreach (var property in properties)
+            {
+                var attribute = (EagerLoadAttribute) property.GetCustomAttribute(typeof(EagerLoadAttribute));
+                if (attribute == null) continue;
+
+                Type innerType = TypeOrElementType(property.PropertyType);
+                attribute.Children = GetEagerLoads(innerType, recursionDepth + 1);
+                attribute.Property = property;
+
+                attributes.Add(attribute);
+            }
+
+            return attributes;
+        }
+
+        private static Type TypeOrElementType(Type type)
+        {
+            var interfaces = type.GetInterfaces()
+                .Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(IEnumerable<>)).ToArray();
+
+            return interfaces.Length == 1 ? interfaces.Single().GenericTypeArguments[0] : type;
+        }
+
         private Type GetResourceDefinitionType(Type entityType) => typeof(ResourceDefinition<>).MakeGenericType(entityType);
 
         private void AssertEntityIsNotAlreadyDefined(Type entityType)

src/JsonApiDotNetCore/Data/DefaultResourceRepository.cs

@@ -47,9 +47,14 @@ public DefaultResourceRepository(
         }
 
         /// <inheritdoc />
-        public virtual IQueryable<TResource> Get() => _dbSet;
+        public virtual IQueryable<TResource> Get()
+        {
+            var resourceContext = _resourceGraph.GetResourceContext<TResource>();
+            return EagerLoad(_dbSet, resourceContext.EagerLoads);
+        }
+
         /// <inheritdoc />
-        public virtual IQueryable<TResource> Get(TId id) => _dbSet.Where(e => e.Id.Equals(id));
+        public virtual IQueryable<TResource> Get(TId id) => Get().Where(e => e.Id.Equals(id));
 
         /// <inheritdoc />
         public virtual IQueryable<TResource> Select(IQueryable<TResource> entities, IEnumerable<AttrAttribute> fields = null)
@@ -279,6 +284,19 @@ public virtual async Task<bool> DeleteAsync(TId id)
             return true;
         }
 
+        private IQueryable<TResource> EagerLoad(IQueryable<TResource> entities, IEnumerable<EagerLoadAttribute> attributes, string chainPrefix = null)
+        {
+            foreach (var attribute in attributes)
+            {
+                string path = chainPrefix != null ? chainPrefix + "." + attribute.Property.Name : attribute.Property.Name;
+                entities = entities.Include(path);
+
+                entities = EagerLoad(entities, attribute.Children, path);
+            }
+
+            return entities;
+        }
+
         public virtual IQueryable<TResource> Include(IQueryable<TResource> entities, IEnumerable<RelationshipAttribute> inclusionChain = null)
         {
             if (inclusionChain == null || !inclusionChain.Any())
@@ -288,10 +306,15 @@ public virtual IQueryable<TResource> Include(IQueryable<TResource> entities, IEn
 
             string internalRelationshipPath = null;
             foreach (var relationship in inclusionChain)
-                internalRelationshipPath = (internalRelationshipPath == null)
+            {
+                internalRelationshipPath = internalRelationshipPath == null
                     ? relationship.RelationshipPath
                     : $"{internalRelationshipPath}.{relationship.RelationshipPath}";
 
+                var resourceContext = _resourceGraph.GetResourceContext(relationship.RightType);
+                entities = EagerLoad(entities, resourceContext.EagerLoads, internalRelationshipPath);
+            }
+
             return entities.Include(internalRelationshipPath);
         }
 

src/JsonApiDotNetCore/Internal/ResourceContext.cs

@@ -42,6 +42,11 @@ public class ResourceContext
         /// </summary>
         public List<RelationshipAttribute> Relationships { get; set; }
 
+        /// <summary>
+        /// Related entities that are not exposed as resource relationships.
+        /// </summary>
+        public List<EagerLoadAttribute> EagerLoads { get; set; }
+
         private List<IResourceField> _fields;
         public List<IResourceField> Fields { get { return _fields ??= Attributes.Cast<IResourceField>().Concat(Relationships).ToList();  } }
 

src/JsonApiDotNetCore/Models/Annotation/EagerLoadAttribute.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+
+namespace JsonApiDotNetCore.Models
+{
+    /// <summary>
+    /// Used to unconditionally load a related entity that is not exposed as a json:api relationship.
+    /// </summary>
+    /// <remarks>
+    /// This is intended for calculated properties that are exposed as json:api attributes, which depend on a related entity to always be loaded.
+    /// <example><![CDATA[
+    /// public class User : Identifiable
+    /// {
+    ///     [Attr(isImmutable: true)] 
+    ///     [NotMapped]
+    ///     public string DisplayName => Name.First + " " + Name.Last;
+    /// 
+    ///     public Name Name { get; set; }
+    /// }
+    /// 
+    /// public class Name // not exposed as resource, only database table
+    /// {
+    ///     public string First { get; set; }
+    ///     public string Last { get; set; }
+    /// }
+    /// 
+    /// public class Blog : Identifiable
+    /// {
+    ///     [HasOne]
+    ///     public User Author { get; set; }
+    /// }
+    /// ]]></example>
+    /// </remarks>
+    public sealed class EagerLoadAttribute : Attribute
+    {
+        public PropertyInfo Property { get; internal set; }
+
+        public IList<EagerLoadAttribute> Children { get; internal set; }
+    }
+}

test/IntegrationTests/IntegrationTests.csproj

@@ -11,7 +11,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="$(EFCoreVersion)" />
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
-    <PackageReference Include="xunit" Version="$(XUnitVersion)" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="$(XUnitVersion)" />
+    <PackageReference Include="xunit" Version="$(XUnitVersion)" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="$(XUnitVersion)" />
   </ItemGroup>
 </Project>