Resource inheritance: sparse fieldsets

src/JsonApiDotNetCore/Queries/FieldSelection.cs

@@ -0,0 +1,75 @@
+using System.Text;
+using JetBrains.Annotations;
+using JsonApiDotNetCore.Configuration;
+using JsonApiDotNetCore.Resources.Annotations;
+
+namespace JsonApiDotNetCore.Queries;
+
+/// <summary>
+/// Provides access to sparse fieldsets, per resource type. There's usually just a single resource type, but there can be multiple in case an endpoint
+/// for an abstract resource type returns derived types.
+/// </summary>
+[PublicAPI]
+public sealed class FieldSelection : Dictionary<ResourceType, FieldSelectors>
+{
+    public bool IsEmpty => Values.All(selectors => selectors.IsEmpty);
+
+    public ISet<ResourceType> GetResourceTypes()
+    {
+        return Keys.ToHashSet();
+    }
+
+#pragma warning disable AV1130 // Return type in method signature should be a collection interface instead of a concrete type
+    public FieldSelectors GetOrCreateSelectors(ResourceType resourceType)
+#pragma warning restore AV1130 // Return type in method signature should be a collection interface instead of a concrete type
+    {
+        ArgumentGuard.NotNull(resourceType, nameof(resourceType));
+
+        if (!ContainsKey(resourceType))
+        {
+            this[resourceType] = new FieldSelectors();
+        }
+
+        return this[resourceType];
+    }
+
+    public override string ToString()
+    {
+        var builder = new StringBuilder();
+
+        var writer = new IndentingStringWriter(builder);
+        WriteSelection(writer);
+
+        return builder.ToString();
+    }
+
+    internal void WriteSelection(IndentingStringWriter writer)
+    {
+        using (writer.Indent())
+        {
+            foreach (ResourceType type in GetResourceTypes())
+            {
+                writer.WriteLine($"{nameof(FieldSelectors)}<{type.ClrType.Name}>");
+                WriterSelectors(writer, type);
+            }
+        }
+    }
+
+    private void WriterSelectors(IndentingStringWriter writer, ResourceType type)
+    {
+        using (writer.Indent())
+        {
+            foreach ((ResourceFieldAttribute field, QueryLayer? nextLayer) in GetOrCreateSelectors(type))
+            {
+                if (nextLayer == null)
+                {
+                    writer.WriteLine(field.ToString());
+                }
+                else
+                {
+                    nextLayer.WriteLayer(writer, $"{field.PublicName}: ");
+                }
+            }
+        }
+    }
+}

src/JsonApiDotNetCore/Queries/FieldSelectors.cs

@@ -0,0 +1,70 @@
+using JetBrains.Annotations;
+using JsonApiDotNetCore.Resources.Annotations;
+
+namespace JsonApiDotNetCore.Queries;
+
+/// <summary>
+/// A data structure that contains which fields (attributes and relationships) to retrieve, or empty to retrieve all. In the case of a relationship, it
+/// contains the nested query constraints.
+/// </summary>
+[PublicAPI]
+public sealed class FieldSelectors : Dictionary<ResourceFieldAttribute, QueryLayer?>
+{
+    public bool IsEmpty => !this.Any();
+
+    public bool ContainsReadOnlyAttribute
+    {
+        get
+        {
+            return this.Any(selector => selector.Key is AttrAttribute attribute && attribute.Property.SetMethod == null);
+        }
+    }
+
+    public bool ContainsOnlyRelationships
+    {
+        get
+        {
+            return this.All(selector => selector.Key is RelationshipAttribute);
+        }
+    }
+
+    public bool ContainsField(ResourceFieldAttribute field)
+    {
+        ArgumentGuard.NotNull(field, nameof(field));
+
+        return ContainsKey(field);
+    }
+
+    public void IncludeAttribute(AttrAttribute attribute)
+    {
+        ArgumentGuard.NotNull(attribute, nameof(attribute));
+
+        this[attribute] = null;
+    }
+
+    public void IncludeAttributes(IEnumerable<AttrAttribute> attributes)
+    {
+        ArgumentGuard.NotNull(attributes, nameof(attributes));
+
+        foreach (AttrAttribute attribute in attributes)
+        {
+            this[attribute] = null;
+        }
+    }
+
+    public void IncludeRelationship(RelationshipAttribute relationship, QueryLayer? queryLayer)
+    {
+        ArgumentGuard.NotNull(relationship, nameof(relationship));
+
+        this[relationship] = queryLayer;
+    }
+
+    public void RemoveAttributes()
+    {
+        while (this.Any(pair => pair.Key is AttrAttribute))
+        {
+            ResourceFieldAttribute field = this.First(pair => pair.Key is AttrAttribute).Key;
+            Remove(field);
+        }
+    }
+}

src/JsonApiDotNetCore/Queries/IndentingStringWriter.cs

@@ -0,0 +1,41 @@
+using System.Text;
+
+namespace JsonApiDotNetCore.Queries;
+
+internal sealed class IndentingStringWriter : IDisposable
+{
+    private readonly StringBuilder _builder;
+
+    private int _indentDepth;
+
+    public IndentingStringWriter(StringBuilder builder)
+    {
+        _builder = builder;
+    }
+
+    public void WriteLine(string? line)
+    {
+        if (_indentDepth > 0)
+        {
+            _builder.Append(new string(' ', _indentDepth * 2));
+        }
+
+        _builder.AppendLine(line);
+    }
+
+    public IndentingStringWriter Indent()
+    {
+        WriteLine("{");
+        _indentDepth++;
+        return this;
+    }
+
+    public void Dispose()
+    {
+        if (_indentDepth > 0)
+        {
+            _indentDepth--;
+            WriteLine("}");
+        }
+    }
+}

src/JsonApiDotNetCore/Queries/Internal/Parsing/SparseFieldTypeParser.cs

@@ -37,14 +37,14 @@ private ResourceType ParseSparseFieldTarget()
 
         EatSingleCharacterToken(TokenKind.OpenBracket);
 
-        ResourceType resourceType = ParseResourceName();
+        ResourceType resourceType = ParseResourceType();
 
         EatSingleCharacterToken(TokenKind.CloseBracket);
 
         return resourceType;
     }
 
-    private ResourceType ParseResourceName()
+    private ResourceType ParseResourceType()
     {
         if (TokenStack.TryPop(out Token? token) && token.Kind == TokenKind.Text)
         {