Code First：Data Anotation (2)

示例一

本例演示與索引有關的內容，模型：

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace DataAnnotations
{
    public class Post
    {
        public int Id { get; set; }
        public string Title { get; set; }

        [Index("PostRatingIndex")]
        public int BlogId { get; set; }
    }

    public class User
    {
        public int UserId { get; set; }

        [Index(IsUnique = true)]
        [StringLength(200)]
        public string Username { get; set; }

        public string DisplayName { get; set; }
    }

    public class Cell
    {
        public int Id { get; set; }
        public string Content { get; set; }

        [Index("IX_Location", 1, IsUnique = true)]
        public int Row { get; set; }

        [Index("IX_Location", 2)]
        [StringLength(5)]
        public string Column { get; set; }
    }
}

生成的數據庫表代碼爲：

------------------------------------------
CREATE TABLE [dbo].[Posts] (
    [Id]     INT            IDENTITY (1, 1) NOT NULL,
    [Title]  NVARCHAR (MAX) NULL,
    [BlogId] INT            NOT NULL,
    CONSTRAINT [PK_dbo.Posts] PRIMARY KEY CLUSTERED ([Id] ASC)
);
GO
CREATE NONCLUSTERED INDEX [PostRatingIndex] ON [dbo].[Posts]([BlogId] ASC);
GO

------------------------------------------
CREATE TABLE [dbo].[Users] (
    [UserId]      INT            IDENTITY (1, 1) NOT NULL,
    [Username]    NVARCHAR (200) NULL,
    [DisplayName] NVARCHAR (MAX) NULL,
    CONSTRAINT [PK_dbo.Users] PRIMARY KEY CLUSTERED ([UserId] ASC)
);
GO
CREATE UNIQUE NONCLUSTERED INDEX [IX_Username]
    ON [dbo].[Users]([Username] ASC);
GO

------------------------------------------
CREATE TABLE [dbo].[Cells] (
    [Id]      INT            IDENTITY (1, 1) NOT NULL,
    [Content] NVARCHAR (MAX) NULL,
    [Row]     INT            NOT NULL,
    [Column]  NVARCHAR (5)   NULL,
    CONSTRAINT [PK_dbo.Cells] PRIMARY KEY CLUSTERED ([Id] ASC)
);
GO
CREATE UNIQUE NONCLUSTERED INDEX [IX_Location]
    ON [dbo].[Cells]([Row] ASC, [Column] ASC);
GO

Post類演示了在BlogId上定義一個名爲PostRatingIndex的索引。

User類演示瞭如何定義一個惟一索引，注意這裏沒有指定索引的名稱，系統按照格式IX_PropertyName生成索引名稱。

Cell類演示多列索引，給每一個列指定相同的名稱，若是有索引選項要修改，只須要在第一個屬性上指定。

對字符串string類型的屬性創建索引，須要指定其長度，長度不能大於某個值。

 示例二

本例演示外鍵，模型代碼：

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace DataAnnotations
{
    public class Blog
    {
        [Key]
        public int PrimaryKey { get; set; }

        public string Title { get; set; }

        //導航屬性
        public virtual ICollection<Post> Posts { get; set; }
    }

    public class Post
    {
        public int Id { get; set; }
        public string Content { get; set; }

        //外鍵
        public int BlogId { get; set; }

        //導航屬性
        [ForeignKey("BlogId")]
        public Blog Blog { get; set; }
    }
}

這裏，Blog的主鍵沒有遵照主鍵的命名約定，在Post類的導航屬性Blog上指定外鍵屬性，其參數"BlogId"指的是Post類成員BlogId是外鍵列。

生成的數據庫代碼：

-----------------------------------------------------------------------------------------
CREATE TABLE [dbo].[Blogs] (
    [PrimaryKey] INT            IDENTITY (1, 1) NOT NULL,
    [Title]      NVARCHAR (MAX) NULL,
    CONSTRAINT [PK_dbo.Blogs] PRIMARY KEY CLUSTERED ([PrimaryKey] ASC)
);

-----------------------------------------------------------------------------------------
CREATE TABLE [dbo].[Posts] (
    [Id]      INT            IDENTITY (1, 1) NOT NULL,
    [Content] NVARCHAR (MAX) NULL,
    [BlogId]  INT            NOT NULL,
    CONSTRAINT [PK_dbo.Posts] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_dbo.Posts_dbo.Blogs_BlogId] FOREIGN KEY ([BlogId]) REFERENCES [dbo].[Blogs] ([PrimaryKey]) ON DELETE CASCADE
);


GO
CREATE NONCLUSTERED INDEX [IX_BlogId]
    ON [dbo].[Posts]([BlogId] ASC);

EF框架默認爲外鍵列添加索引，以加快檢索速度。

如今，將Post類中的ForeignKey標記從導航屬性移動到外鍵屬性上，微調代碼：

    public class Post
    {
        public int Id { get; set; }
        public string Content { get; set; }

        //外鍵
        [ForeignKey("MyBlog")]
        public int BlogId { get; set; }

        //導航屬性
        public Blog MyBlog { get; set; }
    }

 

再次查看生成的數據庫表：

CREATE TABLE [dbo].[Posts] (
    [Id]      INT            IDENTITY (1, 1) NOT NULL,
    [Content] NVARCHAR (MAX) NULL,
    [BlogId]  INT            NOT NULL,
    CONSTRAINT [PK_dbo.Posts] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_dbo.Posts_dbo.Blogs_BlogId] FOREIGN KEY ([BlogId]) REFERENCES [dbo].[Blogs] ([PrimaryKey]) ON DELETE CASCADE
);


GO
CREATE NONCLUSTERED INDEX [IX_BlogId]
    ON [dbo].[Posts]([BlogId] ASC);

可見生成的代碼是同樣的，因而可知，外鍵標記就是在依賴表中創建外鍵屬性與導航屬性之間對應關聯的。

示例三

本示例演示反轉屬性註解，此註解用於兩個實體間有多個關係的狀況，如一個文檔有建立者，有更新者，這二者都是人。此時以下定義模型：

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace DataAnnotations
{
    public class Person
    {
        public int Id { get; set; }
        [Index(IsUnique =true),StringLength(50)]
        public string Name { get; set; }

        //導航屬性
        [InverseProperty("CreatedBy")]
        public List<Document> CreatedDocuments { get; set; }

        [InverseProperty("UpdatedBy")]
        public List<Document> UpdatedDocuments { get; set; }
    }

    public class Document
    {
        public int Id { get; set; }
        public string Content { get; set; }        

        //導航屬性
        public Person CreatedBy { get; set; }
        public Person UpdatedBy { get; set; }
    }
}

在Person類的CreatedDocuments上有標記[InverseProperty("CreatedBy")]，而且此屬性是Document類型的集合，則能夠翻譯成Person類的CreatedDocuments導航屬性是Document類的CreatedBy導航屬性的反屬性。

下面是生成的數據庫：

CREATE TABLE [dbo].[People] (
    [Id]   INT           IDENTITY (1, 1) NOT NULL,
    [Name] NVARCHAR (50) NULL,
    CONSTRAINT [PK_dbo.People] PRIMARY KEY CLUSTERED ([Id] ASC)
);


GO
CREATE UNIQUE NONCLUSTERED INDEX [IX_Name]
    ON [dbo].[People]([Name] ASC);

--------------------------------------------------------------------------------------
CREATE TABLE [dbo].[Documents] (
    [Id]           INT            IDENTITY (1, 1) NOT NULL,
    [Content]      NVARCHAR (MAX) NULL,
    [CreatedBy_Id] INT            NULL,
    [UpdatedBy_Id] INT            NULL,
    CONSTRAINT [PK_dbo.Documents] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_dbo.Documents_dbo.People_CreatedBy_Id] FOREIGN KEY ([CreatedBy_Id]) REFERENCES [dbo].[People] ([Id]),
    CONSTRAINT [FK_dbo.Documents_dbo.People_UpdatedBy_Id] FOREIGN KEY ([UpdatedBy_Id]) REFERENCES [dbo].[People] ([Id])
);


GO
CREATE NONCLUSTERED INDEX [IX_CreatedBy_Id]
    ON [dbo].[Documents]([CreatedBy_Id] ASC);


GO
CREATE NONCLUSTERED INDEX [IX_UpdatedBy_Id]
    ON [dbo].[Documents]([UpdatedBy_Id] ASC);

 EF在外鍵表Documents中生成外鍵列的名字爲：導航屬性_Id。