实体框架代码第一外键添加索引

Question

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.

Answer 1

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.