c# - 解决了-也许？如何使用相关 DTO 的嵌套列表返回 DTO 列表

Question

在不使用 Automapper 的情况下，我试图将 DTO 列表映射到 DTO 列表的每个元素中。特别是在这个例子中，我希望 API 返回一个父母列表，其中每个父母都包含它的孩子列表和宠物列表。

我有一个 EF Core 项目，其中包含以下模型（使用完全定义的关系）并且存在于更大的数据库中。

有一个 Parent 对象，它有许多 Pet 对象和许多 Child 对象，如下所示：

EF 核心模型

    public class Parent
    {
        public int ParentId { get; set; }
        public string Name { get; set; }

        public List<Child> Children { get; set; }
        public List<Pet> Pets { get; set; }
    }

    public class Child
    {
        public int ChildId { get; set; }
        public string Name { get; set; }

        public int ParentId { get; set; }
        public Parent Parent { get; set; }
    }

    public class Pet
    {
        public int PetId { get; set; }
        public string Name { get; set; }

        public int ParentId { get; set; }
        public Parent Parent { get; set; }
    }

在不使用 Automapper 的情况下，我试图在控制器中使用 DTO 来发送数据。

我已按如下方式设置 DTO：

DTO

    public class ParentDTO
    {
        public int ParentId { get; set; }
        public string Name { get; set; }

        //Should these be List<> or IEnumerable<>?
        public IEnumerable<ChildDTO> Children { get; set; }
        public IEnumerable<PetDTO> Pets { get; set; }
    }

    public class ChildDTO
    {
        public int ChildId { get; set; }
        public string Name { get; set; }
    }

    public class PetDTO
    {
        public int PetId { get; set; }
        public string Name { get; set; }
    }

目前我的控制器看起来像这样：

控制器尝试 1

        // GET: api/Parents/
        [HttpGet]
        public IEnumerable<ParentDTO> GetParents()
        {

            var parents = from pa in _context.Parents
                          select new ParentDTO()
                          {
                              Name = pa.Name
                          };

            return parents;
        }

        // GET: api/Parents/GetParentsWith
        [HttpGet("[action]")]
        public IEnumerable<ParentDTO> GetParentsWith()
        {

            var parents = from pa in _context.Parents
                          select new ParentDTO()
                          {
                              Name = pa.Name,
                              //Not sure how to correctly do this below...
                              Children = (from c in _context.Children.Where(c => c.ParentId == pa.ParentId)
                                          select new ChildDTO()
                                          {
                                              Name = c.Name
                                          }),
                              Pets = (from pe in _context.Pets.Where(pet => pet.ParentId == pa.ParentId)
                                      select new PetDTO()
                                      {
                                          Name = pe.Name
                                      })
                          };

            return parents;
        }

我的GET: api/Parents/作品很好（因为我没有尝试制作嵌套列表），但是我如何像我想要做的那样将相关的子项和宠物项添加到父母 DTO 中GET: api/Parents/GetParentsWith？

尝试这样做会出现错误：

Microsoft.Data.SqlClient.SqlException (0x80131904): Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
....
...

我也试过：

控制器尝试 2

        // GET: api/Parents/GetParentsWith
        [HttpGet("[action]")]
        public IEnumerable<ParentDTO> GetParentsWith()
        {

            var parents = from pa in _context.Parents
                          select new ParentDTO()
                          {
                              Name = pa.Name,
                              Children = (from c in pa.Children
                                          select new ChildDTO()
                                          {
                                              Name = c.Name
                                          }),
                              Pets = (from pe in pa.Pets
                                      select new PetDTO()
                                      {
                                          Name = pe.Name
                                      })
                          };

            return parents;
        }

这也给出了错误：

Microsoft.Data.SqlClient.SqlException (0x80131904): Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
....
...

我也试过：

控制器尝试 3

        // GET: api/Parents/GetParentsWith
        [HttpGet("[action]")]
        public IEnumerable<ParentDTO> GetParentsWith()
        {

            var parents = from pa in _context.Parents
                          select new ParentDTO()
                          {
                              ParentId = pa.ParentId,
                              Name = pa.Name
                          };

            foreach (ParentDTO parent in parents)
            {
                var children = from child in _context.Children where child.ParentId == parent.ParentId
                               select new ChildDTO()
                               {
                                   ChildId = child.ChildId,
                                   Name = child.Name
                               };

                var pets = from pet in _context.Pets
                           where pet.ParentId == parent.ParentId
                           select new PetDTO()
                           {
                               PetId = pet.PetId,
                               Name = pet.Name
                           };

                parent.Children = children;
                parent.Pets = pets;

            return parents;
        }

这不会引发任何错误，所以也许我在这里的正确轨道上，不幸的是它只是返回 null 我期望一组孩子或宠物的地方：

[
    {
        "parentId": 1,
        "name": "Ronald",
        "children": null,
        "pets": null
    },
    {
        "parentId": 2,
        "name": "Benjamin",
        "children": null,
        "pets": null
    },
    {
        "parentId": 3,
        "name": "Sally",
        "children": null,
        "pets": null
    },
    {
        "parentId": 4,
        "name": "Foobar",
        "children": null,
        "pets": null
    }
]

解决了！但我做对了吗？

我注意到parents它是一个 IQueryable，因此 foreach 中的分配没有按我预期的那样工作......我想我需要了解一些关于 IQueryable、IEnumerable 等的知识。

        // GET: api/Parents/GetParentsWith
        [HttpGet("[action]")]
        public ask<ActionResult<IEnumerable<ParentDTO>>> GetParentsWith()
        {

            var parents = (from pa in _context.Parents
                          select new ParentDTO()
                          {
                              ParentId = pa.ParentId,
                              Name = pa.Name
                          }).ToListAsync();

            foreach (ParentDTO parent in await parents)
            {
                var children = from child in _context.Children where child.ParentId == parent.ParentId
                               select new ChildDTO()
                               {
                                   ChildId = child.ChildId,
                                   Name = child.Name
                               };

                var pets = from pet in _context.Pets
                           where pet.ParentId == parent.ParentId
                           select new PetDTO()
                           {
                               PetId = pet.PetId,
                               Name = pet.Name
                           };

                parent.Children = children;
                parent.Pets = pets;
            }

            return parents;
        }

标签： c#asp.net-corelinq-to-sqlentity-framework-coredto