1.什么是Fluent API?EF中内嵌的约定将POCO类映射到表。但是,有时您无法或不想遵守这些约定,需要将实体映射到约定指示外的其他对象,所以Fluent API和注解都是一种方法,这两种方法是用来配置EF在映射属性时绕开约定。Code first fluent API最常访问通过重写OnModelCreating方法在派生DbContext。 2.包含属性和排除属性按照约定,数据模型中都包含一个getter和一个setter公共属性。 2.1包含属性包含属性官网解释有点难以理解,我个人认为在OnModelCreating方法配置包含Blog模型,那么当我们调用Blog模型读写数据时候就会从连接数据库中读写对应Blog表。 protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Blog>(); } 2.2排除属性如果你不想往BlogMetadata上读写数据,可以使用数据批注或者fluent API从模型中排除该实体类型。 2.2.1数据批注namespace EFModeling.DataAnnotations.IgnoreType { class MyContext : DbContext { public DbSet<Blog> Blogs { get; set; } } public class Blog { public int BlogId { get; set; } public string Url { get; set; } public BlogMetadata Metadata { get; set; } } //读写不映射该实体 [NotMapped] public class BlogMetadata { public DateTime LoadedFromDatabase { get; set; } } } 2.2.2Fluent APInamespace EFModeling.FluentAPI.IgnoreType { class MyContext : DbContext { public DbSet<Blog> Blogs { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder) { //Ignore方法就是读写不映射该实体 modelBuilder.Ignore<BlogMetadata>(); } } public class Blog { public int BlogId { get; set; } public string Url { get; set; } public BlogMetadata Metadata { get; set; } } public class BlogMetadata { public DateTime LoadedFromDatabase { get; set; } } } 3.主键使用关系型数据库时候,都会涉及到主键概念,用作每个实体实例的主要唯一标识符。 3.1数据批注namespace EFModeling.DataAnnotations.KeySingle { class MyContext : DbContext { public DbSet<Car> Cars { get; set; } } class Car { //设置LicensePlate为主键 [Key] public string LicensePlate { get; set; } public string Make { get; set; } public string Model { get; set; } } } 3.2Fluent APInamespace EFModeling.FluentAPI.KeySingle { class MyContext : DbContext { public DbSet<Car> Cars { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Car>() //设置LicensePlate为主键 .HasKey(c => c.LicensePlate); } } class Car { public string LicensePlate { get; set; } public string Make { get; set; } public string Model { get; set; } } } 4.生成值有三个可用于属性的值生成模式: USE [Blogging] GO /****** Object: Trigger [dbo].[Blog_Update_Trigger] Script Date: 2019/10/22 16:18:13 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO ALTER TRIGGER [dbo].[Blog_Update_Trigger] ON [dbo].[Blog] AFTER UPDATE AS BEGIN SET NOCOUNT ON; IF ((SELECT TRIGGER_NESTLEVEL()) > 1) RETURN; DECLARE @Id INT SELECT @Id = INSERTED.BlogId FROM INSERTED UPDATE dbo.Blog SET Updatetime = GETDATE() WHERE BlogId = @Id END 4.1数据批注4.1.1无值生成public class Blog { [DatabaseGenerated(DatabaseGeneratedOption.None)] public int BlogId { get; set; } public string Url { get; set; } } 4.1.2在添加时生成值public class Blog { public int BlogId { get; set; } public string Url { get; set; } [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public DateTime Inserted { get; set; } } 4.1.3在添加或更新时生成值public class Blog { public int BlogId { get; set; } public string Url { get; set; } [DatabaseGenerated(DatabaseGeneratedOption.Computed)] public DateTime LastUpdated { get; set; } } 4.2Fluent API4.2.1无值生成modelBuilder.Entity<Blog>() .Property(b => b.BlogId) .ValueGeneratedNever(); 4.2.2在添加时生成值modelBuilder.Entity<Blog>() .Property(b => b.Inserted) .ValueGeneratedOnAdd(); 4.2.3在添加或更新时生成值modelBuilder.Entity<Blog>() .Property(b => b.LastUpdated) .ValueGeneratedOnAddOrUpdate(); |
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