如何让 self-referencing C# 实体用 JSON.Net 序列化 children？

Question

我很难在 POCO 上获取分层 child 集合进行序列化。这是一个 Azure 移动服务项目。我想出了一个简化的例子来尝试让它工作。

以下是项目中唯一的DTO POCO。请注意名为 Parent 和 Children 的导航属性（标记为虚拟），用于 link 层次结构。

public class Node : EntityData
{
    public Node()
    {
        Children = new List<Node>();
    }

    public string Text { get; set; }

    public string ParentId { get; set; }

    public virtual Node Parent { get; set; }

    public virtual ICollection<Node> Children { get; set; }
}

控制器：

public class NodeController : TableController<Node>
{
    /* BEGIN boilerplate (from Azure Mobile Services project template) */
    protected override void Initialize(HttpControllerContext controllerContext)
    {
        base.Initialize(controllerContext);
        MyContext context = new MyContext();
        DomainManager = new EntityDomainManager<Node>(context, Request, Services);
    }
    /* END boilerplate (from Azure Mobile Services project template) */

    // GET tables/Node
    /// <summary>
    /// Gets all child nodes of a particular node, and their children.
    /// To retrieve the top-level node, pass no id.
    /// </summary>
    /// <param name="id">The id of the node you wish to retrieve.</param>
    /// <returns>The child nodes of a given id.</returns>
    public IQueryable<Node> GetNodes(string id = null)
    {
        return Query().Where(x => x.ParentId == id).Include(x => x.Children);
    }
}

上下文 class:

public class MyContext : DbContext
{
    private const string connectionStringName = "Name=MS_TableConnectionString";

    public MyContext() : base(connectionStringName)
    {
    } 

    public DbSet<Node> Nodes { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Node>()
            .HasMany(t => t.Children)
            .WithOptional(t => t.Parent)
            .HasForeignKey(t => t.ParentId);

        /* BEGIN boilerplate (from Azure Mobile Services project template) */
        string schema = ServiceSettingsDictionary.GetSchemaName();
        if (!string.IsNullOrEmpty(schema))
        {
            modelBuilder.HasDefaultSchema(schema);
        }

        modelBuilder.Conventions.Add(
            new AttributeToColumnAnnotationConvention<TableColumnAttribute, string>(
                "ServiceTableColumn", (property, attributes) => attributes.Single().ColumnType.ToString()));
        /* END boilerplate (from Azure Mobile Services project template) */
    }
}

上下文初始化程序：

public class MyContextInitializer : ClearDatabaseSchemaAlways<MyContext>
{
    protected override void Seed(MyContext context)
    {
        var node0_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Node 0-1" };
        var node0_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Node 0-2" };

        var node1_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 1-1", Parent = node0_1 };
        var node1_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 1-2", Parent = node0_1 };

        var node2_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 2-1", Parent = node0_2 };
        var node2_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 2-2", Parent = node0_2 };

        node0_1.Children.Add(node1_1);
        node0_1.Children.Add(node1_2);

        node0_2.Children.Add(node2_1);
        node0_2.Children.Add(node2_2);

        List<Node> nodes = new List<Node>
        {
            node0_1,
            node0_2
        };

        context.Set<Node>().AddRange(nodes);

        base.Seed(context);
    }
}

为什么 Children 从未出现在结果中？

[
    {
        "$id": "1",
        "id": "2c381538-b8e9-4b7c-b25d-7f6fd8cd373e",
        "parentId": null,
        "text": "Node 0-2"
    },
    {
        "$id": "2",
        "id": "695af179-aa27-45d3-9299-a96c5e719448",
        "parentId": null,
        "text": "Node 0-1"
    }
]

...即使生成的 API 文档样本表明应该 Children:

[
    {
        "$id": "1",
        "text": "sample string 1",
        "parentId": "sample string 2",
        "parent": {
          "$ref": "1"
        },
        "children": [
          {
            "$ref": "1"
          },
          {
            "$ref": "1"
          },
          {
            "$ref": "1"
          }
        ],
        "id": "sample string 3",
        "__version": "QEBA",
        "__createdAt": "2015-06-26T01:46:14.108Z",
        "__updatedAt": "2015-06-26T01:46:14.108Z",
        "__deleted": true
      },
      {
        "$ref": "1"
      },
      {
        "$ref": "1"
      }
    ]

Answer 1

Finally figured it out. Just had to change the return type of the controller's GetNodes() method from IQueryable<Node> to IEnmerable<Node>. I still don't know exactly why, but I'm glad it's working. Now I can move on to the important stuff: modifying my actual service, and then consuming it in the Xamarin app.

Revised method signature (threw in some async for good measure):

public async Task<IEnumerable<Node>> GetNode(string id = null)
{
    return await Query()
        .Where(x => x.ParentId == id)
        .Include(x => x.Children)
        .ToListAsync();
}

结果：

[
  {
    "$id": "1",
    "children": [
      {
        "$id": "2",
        "children": [],
        "parent": {
          "$ref": "1"
        },
        "text": "Item 1-2",
        "parentId": "6a616abe-8328-4ca0-92e4-de0734101f2f",
        "id": "398cf2e6-dbfb-4fe1-8555-13090885292f",
        "__version": "AAAAAAABbzQ=",
        "__createdAt": "2015-06-26T21:07:31.466Z",
        "__updatedAt": "2015-06-26T21:07:31.466Z"
      },
      {
        "$id": "3",
        "children": [],
        "parent": {
          "$ref": "1"
        },
        "text": "Item 1-1",
        "parentId": "6a616abe-8328-4ca0-92e4-de0734101f2f",
        "id": "6560562b-0694-4436-bc50-08ead5af29e0",
        "__version": "AAAAAAABbzY=",
        "__createdAt": "2015-06-26T21:07:31.521Z",
        "__updatedAt": "2015-06-26T21:07:31.521Z"
      }
    ],
    "text": "Node 0-1",
    "id": "6a616abe-8328-4ca0-92e4-de0734101f2f",
    "__version": "AAAAAAABbzI=",
    "__createdAt": "2015-06-26T21:07:31.382Z",
    "__updatedAt": "2015-06-26T21:07:31.399Z"
  },
  {
    "$id": "4",
    "children": [
      {
        "$id": "5",
        "children": [],
        "parent": {
          "$ref": "4"
        },
        "text": "Item 2-1",
        "parentId": "fdf50979-e191-41c7-b6c4-c2067cd88dc9",
        "id": "9417571f-f89e-4183-8c14-ba7da3629624",
        "__version": "AAAAAAABbzo=",
        "__createdAt": "2015-06-26T21:07:31.634Z",
        "__updatedAt": "2015-06-26T21:07:31.634Z"
      },
      {
        "$id": "6",
        "children": [],
        "parent": {
          "$ref": "4"
        },
        "text": "Item 2-2",
        "parentId": "fdf50979-e191-41c7-b6c4-c2067cd88dc9",
        "id": "b077165c-1e3e-456f-b4c5-6b116941ba30",
        "__version": "AAAAAAABbzw=",
        "__createdAt": "2015-06-26T21:07:31.693Z",
        "__updatedAt": "2015-06-26T21:07:31.694Z"
      }
    ],
    "text": "Node 0-2",
    "id": "fdf50979-e191-41c7-b6c4-c2067cd88dc9",
    "__version": "AAAAAAABbzg=",
    "__createdAt": "2015-06-26T21:07:31.575Z",
    "__updatedAt": "2015-06-26T21:07:31.575Z"
  }
]

如何让 self-referencing C# 实体用 JSON.Net 序列化 children？

How to get self-referencing C# Entities to serialize children with JSON.Net?

c#

json

entity-framework

azure-mobile-services