实体框架代码第一个外键添加指数 [英] Entity Framework Code First Foreign Key adding Index as well

问题描述

  public class Address 
 {
 ///< summary> 
 ///获取或设置ID。 
 ///< / summary> 
 [Key] 
 [DatabaseGenerated（DatabaseGeneratedOption.Identity）] 
 [Column（Order = 1）] 
 public int Id {get;组; } 
 
 ///< summary> 
 ///获取或设置城镇。 
 ///< / summary> 
 public virtual Town Town {get;组; } 
 
 ///< summary> 
 ///获取或设置paf地址城镇ID。 
 ///< / summary> 
 [Column（Order = 2）] 
 public int TownId {get;组; } 
} 
  

当表创建时，它正在创建一个外键以及一个指数。我不知道为什么，因为这样的索引通常是非常低效的，而对于大的数据库，它引起很多问题。那么为什么它只创建该索引而不是外键。而如何在默认情况下禁用这样的索引创建。

解决方案

这只是一个Entity Framework的约定。如果您不喜欢，那么您可以启用项目的迁移，并将迁移更改为不包括外键。我不同意你的说法，这是低效的。

要启用数据库迁移，请执行以下操作：

1. 在包管理器控制台中，键入启用迁移


2. 在包管理器控制台中，键入添加迁移初始迁移


3. 将迁移迁移添加到Migrations文件夹中，您将看到一个 Up 方法与几个语句。找到添加外键并将其删除的行。


4. 在包管理器控制台中，键入 Update-Database 应用迁移。


5. 对于任何新的更改，重复步骤2-4。

这是假设你还没有数据库，从头开始。

I have simple table definition in EF 6 code-first with simple foreign key.

public class Address
{
        /// <summary>
        /// Gets or sets the id.
        /// </summary>
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        [Column(Order = 1)]
        public int Id { get; set; }

         /// <summary>
        /// Gets or sets the town.
        /// </summary>
        public virtual Town Town { get; set; }

        /// <summary>
        /// Gets or sets the paf address town id.
        /// </summary>
        [Column(Order = 2)]
        public int TownId { get; set; }
}

When the table is created it is creating a foreign key as well as an index. I wonder why, because such index is usually very inefficient, and for big databases it causing a lot of issues. So why it created that index instead of foreign key only. And how to disable by default such index creating.

解决方案

This is just a convention of Entity Framework. If you don't like it, then you can enable migrations on your project and change the migration to not include the foreign key. I disagree with your assertion that it is inefficient, though.

To enable database migrations do the following:

1. In the Package Manager console, type Enable-Migrations
2. In the Package Manager console, type Add-Migration InitialMigration
3. A new migration will be added to the Migrations folder, in it you will see an Up method with a few statements. Find the line that adds the foreign key and remove it.
4. In the Package Manager console, type Update-Database to apply migrations.
5. Repeat steps 2-4 for any new changes that come in.

This is assuming you do not have a database yet and are starting from scratch.

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