ASP.NET Core 2.1 Entity Framework Core 相关数据复制

Question

我正在尝试构建一个 ASP.NET Core API，它返回一个包含一些相关、连接数据的对象。

但是当我使用 Include() 调用 Article 模型时，它会由 EF Core 自动映射。这是有意的，但是.. 发生了意外的映射。

EF Core 为所有对象生成完全映射的对象，从而产生过多的数据。

例如，User 模型具有 Article 属性，当我调用 Article 模型时，User 属性也包含 Article 对象信息。结果，它返回了很多重复的数据。

第一次，我认为它来自

https://docs.microsoft.com/en-us/ef/core/querying/related-data

1. 渴望加载
2. 显式加载
3. 延迟加载

但事实并非如此。

我不知道如何配置 EF Core 不映射里面的所有对象..

*数据库架构和模型

enter image description here

public class Topic
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [HiddenInput(DisplayValue = false)]
    public int TopicId { get; set; }

    [Required]
    [StringLength(20, ErrorMessage = "Title cannot be longer than 20 characters.")]
    public string Title { get; set; }

    [StringLength(200, ErrorMessage = "Description cannot be longer than 200 characters.")]
    public string Description { get; set; }

    public byte[] Picture { get; set; }

    public string PictureMimeType { get; set; }

    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:MM-dd-yyyy}", ApplyFormatInEditMode = true)]
    public DateTime PostDate { get; set; }

    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:MM-dd-yyyy}", ApplyFormatInEditMode = true)]
    public DateTime ModifyDate { get; set; }

    [Display(Name = "Show")]
    public bool ShowFlag { get; set; }

    public int UserId { get; set; }

    public virtual User User { get; set; }

    public virtual ICollection<Article> Articles { get; set; }
}

public class Article
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [HiddenInput(DisplayValue = false)]
    public int ArticleId { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "Title cannot be longer than 100 characters.")]
    public string Title { get; set; }

    public string Content { get; set; }

    [StringLength(10, ErrorMessage = "Category cannot be longer than 10 characters.")]
    public string Category { get; set; } = "Free";

    public byte[] Picture { get; set; }

    public string PictureMimeType { get; set; }

    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:MM-dd-yyyy}", ApplyFormatInEditMode = true)]
    public DateTime PostDate { get; set; }

    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:MM-dd-yyyy}", ApplyFormatInEditMode = true)]
    public DateTime ModifyDate { get; set; }

    public int ReadCount { get; set; }

    [Required]
    [Display(Name = "Show")]
    public bool ShowFlag { get; set; }

    public int TopicId { get; set; }

    public virtual Topic Topic { get; set; }

    public int UserId { get; set; }

    public virtual User User { get; set; }
}

public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [HiddenInput(DisplayValue = false)]
    public int UserId { get; set; }

    [StringLength(20, ErrorMessage = "Name cannot be longer than 20 characters.")]
    public string Name { get; set; }

    [StringLength(255, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    public string Password { get; set; }

    [DataType(DataType.EmailAddress)]
    [EmailAddress]
    public string Email { get; set; }

    [StringLength(20, ErrorMessage = "Title cannot be longer than 20 characters.")]
    public string Title { get; set; }

    [StringLength(20, ErrorMessage = "Phone number cannot be longer than 20 characters.")]
    [DataType(DataType.PhoneNumber)]
    public string Phone { get; set; }

    [StringLength(100, ErrorMessage = "Address cannot be longer than 100 characters.")]
    public string Address { get; set; }

    [StringLength(100, ErrorMessage = "Introduction cannot be longer than 100 characters.")]
    public string Introduction { get; set; }

    [DataType(DataType.Date)]
    public DateTime? Birthdate { get; set; }

    public byte[] Picture { get; set; }

    public string PictureMimeType { get; set; }

    public virtual ICollection<Topic> Topics { get; set; }

    public virtual ICollection<Article> Articles { get; set; }
}

*控制器代码

   var article = await this._context.Articles
     .Include(a => a.User)
     .Include(a => a.Topic)
     .SingleOrDefaultAsync(a => a.ArticleId == id);

*重复数据

{
"articleId": 5,
"title": "Does TaskAll() really wait for all in any case?",
"content": null,
"category": "Threading",
"picture": null,
"pictureMimeType": null,
"postDate": "2018-06-18T07:00:00",
"modifyDate": "2018-06-20T07:47:42.1854485",
"readCount": 101,
"showFlag": true,
"topicId": 1,
"topic": {
    "topicId": 1,
    "title": "C#",
    "description": "About C#",
    "picture": null,
    "pictureMimeType": null,
    "postDate": "2018-05-28T07:00:00",
    "modifyDate": "2018-05-28T23:36:04.701311",
    "showFlag": true,
    "userId": 1,
    "user": {
        "userId": 1,
        "name": "",
        "password": null,
        "email": "",
        "title": "Junior Programmer!!",
        "phone": "",
        "address": "",
        "introduction": "Hey, I'm Jason, most motivated person to be a fullstack programmer! ",
        "birthdate": null,
        "picture": null,
        "pictureMimeType": null,
        "permissionId": 0,
        "permission": null,
        "topics": [],
        "articles": [
            {
                "articleId": 5,
                "title": "Does TaskAll() really wait for all in any case?",
                "content": null,
                "category": "Threading",
                "picture": null,
                "pictureMimeType": null,
                "postDate": "2018-06-18T07:00:00",
                "modifyDate": "2018-06-20T07:47:42.1854485",
                "readCount": 101,
                "showFlag": true,
                "topicId": 1,
                "userId": 1
            }
        ]
    },
    "articles": [
        {
            "articleId": 5,
            "title": "Does TaskAll() really wait for all in any case?",
            "content": null,
            "category": "Threading",
            "picture": null,
            "pictureMimeType": null,
            "postDate": "2018-06-18T07:00:00",
            "modifyDate": "2018-06-20T07:47:42.1854485",
            "readCount": 101,
            "showFlag": true,
            "topicId": 1,
            "userId": 1,
            "user": {
                "userId": 1,
                "name": "",
                "password": null,
                "email": "",
                "title": "Junior Programmer!!",
                "phone": "",
                "address": "",
                "introduction": "Hey, I'm Jason, most motivated person to be a fullstack programmer! ",
                "birthdate": null,
                "picture": null,
                "pictureMimeType": null,
                "topics": [],
                "articles": []
            }
        }
    ]
},
"userId": 1,
"user": {
    "userId": 1,
    "name": "",
    "password": null,
    "email": "",
    "title": "Junior Programmer!!",
    "phone": "",
    "address": "",
    "introduction": "Hey, I'm Jason, most motivated person to be a fullstack programmer! ",
    "birthdate": null,
    "picture": null,
    "pictureMimeType": null,
    "topics": [
        {
            "topicId": 1,
            "title": "C#",
            "description": "About C#",
            "picture": null,
            "pictureMimeType": null,
            "postDate": "2018-05-28T07:00:00",
            "modifyDate": "2018-05-28T23:36:04.701311",
            "showFlag": true,
            "userId": 1,
            "articles": [
                {
                    "articleId": 5,
                    "title": "Does TaskAll() really wait for all in any case?",
                    "content": null,
                    "category": "Threading",
                    "picture": null,
                    "pictureMimeType": null,
                    "postDate": "2018-06-18T07:00:00",
                    "modifyDate": "2018-06-20T07:47:42.1854485",
                    "readCount": 101,
                    "showFlag": true,
                    "topicId": 1,
                    "userId": 1
                }
            ]
        }
    ],
    "articles": [
        {
            "articleId": 5,
            "title": "Does TaskAll() really wait for all in any case?",
            "content": null,
            "category": "Threading",
            "picture": null,
            "pictureMimeType": null,
            "postDate": "2018-06-18T07:00:00",
            "modifyDate": "2018-06-20T07:47:42.1854485",
            "readCount": 101,
            "showFlag": true,
            "topicId": 1,
            "topic": {
                "topicId": 1,
                "title": "C#",
                "description": "About C#",
                "picture": null,
                "pictureMimeType": null,
                "postDate": "2018-05-28T07:00:00",
                "modifyDate": "2018-05-28T23:36:04.701311",
                "showFlag": true,
                "userId": 1,
                "articles": []
            },
            "userId": 1
        }
    ]
}

}

Answer 1

实际上，没有“重复”的数据。

当执行以下查询时：

var article = await this._context.Articles
     .Include(a => a.User)
     .Include(a => a.Topic)
     .SingleOrDefaultAsync(a => a.ArticleId == id);

幕后的 sql 将是：

SELECT TOP(1) 
    [a].[ArticleId], [a].[Category], [a].[Content], [a].[ModifyDate], [a].[Picture], [a].[PictureMimeType], [a].[PostDate],[a].[ReadCount], [a].[ShowFlag], [a].[Title], 
    [a].[TopicId], [a].[UserId], 

    [a.Topic].[TopicId], [a.Topic].[Description], [a.Topic].[ModifyDate], [a.Topic].[Picture], [a.Topic].[PictureMimeType], [a.Topic].[PostDate], [a.Topic].[ShowFlag], [a.Topic].[Title],[a.Topic].[UserId], 

    [a.User].[UserId], [a.User].[Address], [a.User].[Birthdate], [a.User].[Email], [a.User].[Introduction], [a.User].[Name], [a.User].[Password], [a.User].[Phone], [a.User].[Picture], [a.User].[PictureMimeType], [a.User].[Title]
FROM [Article] AS [a]
INNER JOIN [Topics] AS [a.Topic] ON [a].[TopicId] = [a.Topic].[TopicId]
INNER JOIN [Users] AS [a.User] ON [a].[UserId] = [a.User].[UserId]
WHERE [a].[ArticleId] = @__id_0

SQL 不会加载任何额外的记录。假设一个用户有两篇文章：

Article1 : { ArticleId=1, UserId=1}
Article3 : { ArticleId=3, UserId=1}

上面的查询只会加载一篇文章。

当记录从服务器加载到内存中时，EFCore 知道 User 和 Articles 之间存在1-to-many 的关系，并开始将 user 对象设置为 article 的导航属性。用户实体和主题实体之间也是如此。所有这些都在记忆中完成。

如您所见，没有从数据库中检索到额外记录，内存中也没有重复数据。

让你感到困惑的是序列化到客户端的数据。不过，这确实有道理。由于纯字符串没有引用/指针的概念，因此很难用 json 表示对象之间的关系。

顺便说一句，没有必要用两个几乎相同的属性来装饰你的 User 的 Email 属性：

[DataType(DataType.EmailAddress)]
[EmailAddress]
public string Email { get; set; }

迁移数据库时会出现“两个相同的自定义属性”的错误。