警告

This documentation is for EF7 onwards. For EF6.x and earlier release see http://msdn.com/data/ef. 本文档是基于EF7版本.对于EF6.x及更早的版本请参见 http://msdn.com/data/ef.

注解

This article uses EF 7.0.0-rc1 which is the latest pre-release available on NuGet.org. You can find nightly builds of the EF7 code base hosted on https://www.myget.org/F/aspnetvnext/ but we do not maintain up-to-date documentation for nightly builds.

注解

The configuration in this section is applicable to relational databases in general. The extension methods shown here will become available when you install a relational database provider (due to the shared EntityFramework.Relational package).

Sequences

A sequence generates a sequential numeric values in the database. Sequences are not associated with a specific table.

Conventions

By convention, sequences are not introduced in to the model.

Data Annotations

You can not configure a sequence using Data Annotations.

Fluent API

You can use the Fluent API to create a sequence in the model.

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    class MyContext : DbContext
    {
        public DbSet<Order> Orders { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.HasSequence<int>("OrderNumbers");
        }
    }

    public class Order

You can also configure additional aspect of the sequence, such as its schema, start value, and increment.

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    class MyContext : DbContext
    {
        public DbSet<Order> Orders { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.HasSequence<int>("OrderNumbers", schema: "shared")
                .StartsAt(1000)
                .IncrementsBy(5);
        }
    }

Once a sequence is introduced, you can use it to generate values for properties in your model. For example, you can use Default Values to insert the next value from the sequence.

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    class MyContext : DbContext
    {
        public DbSet<Order> Orders { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.HasSequence<int>("OrderNumbers", schema: "shared")
                .StartsAt(1000)
                .IncrementsBy(5);

            modelBuilder.Entity<Order>()
                .Property(o => o.OrderNo)
                .HasDefaultValueSql("NEXT VALUE FOR shared.OrderNumbers");
        }
    }

    public class Order
    {
        public int OrderId { get; set; }
        public int OrderNo { get; set; }
        public string Url { get; set; }
    }