EF Code First 入门

1、安装 Entity Framework

在 VS 编辑中点击 Tools -> Library Package Manager -> Package Manager Console

在 Package Manager Console 窗口中执行下面语句，安装最新版 Entity Framework：

PM> Install-Package EntityFramework

安装完成之后，将自动添加对 EntityFramework 的引用，并自动添加 App.config 和 packages.config 文件。

2、简单配置

在生成的配置文件中，加入如下代码，修改数据库连接信息：

View Code

3、实体类

View Code

    public class Category
    {
        public string CategoryId { set; get; }
        public string Name { set; get; }
        public virtual ICollection<Product> Products { set; get; }
    }

    public class Product
    {
        public int ProductId { set; get; }
        public string Name { set; get; }
        public string CategoryId { set; get; }
        public virtual Category Category { set; get; }

4、数据库 Context

View Code

using System.Data.Entity; // 引用命名空间

namespace EFTest
{
    public class EFTestContext : DbContext
    {
        public EFTestContext()
            : base("EFTestContext") // 配置文件中连接字符串 Key 值
        {
        }

        public DbSet<Category> Categories { set; get; }
        public DbSet<Product> Products { set; get; }
    }

5、读写数据

View Code

        static void Main(string[] args)
        {
            //新增 Category
            using (var db = new EFTestContext())
            {
                var food = new Category
                {
                    CategoryId = "A002",
                    Name = "文具"
                };
                db.Categories.Add(food);
                int recordsAffected = db.SaveChanges();
            }

            using (var db = new EFTestContext())
            {
                //查询 Category
                var category = db.Categories.Find("A003");
                if (category == null)
                {
                    category = new Category { CategoryId="A003", Name="体育" };
                    db.Categories.Add(category);
                }

                //新增 Product
                var product = new Product { Name="篮球", Category=category };
                db.Products.Add(product);
                int recordsAffected = db.SaveChanges();

                //使用LINQ查询 Product
                var allProduct = from p in db.Products
                                 where p.CategoryId == "A003"
                                 orderby p.Name
                                 select p;
                foreach (var item in allProduct)
                {
                    Console.WriteLine(item.Name);
                }
            }
            Console.ReadKey();

6、数据初始化或实体类改变

View Code

    public class DbInitailizer
    {
        /// <summary>
        /// 执行对数据库的初始化操作。
        /// </summary>

        public static void Initialize()
        {
            using (EFTestContext db = new EFTestContext())
            {
                if (db.Database.Exists())
                {
                    db.Database.Delete();
                }
                db.Database.Create();
                //数据初始化操作
            }
        }

7、数据注释 Annotations

View Code

//使用注解，需引用该命名空间
using System.ComponentModel.DataAnnotations;

namespace EFTest.EFCodeFirst
{
    public class Supplier
    {
        [Key]
        public string SupplierCode { get; set; }
        public string Name { get; set; }
    }

EF 所支持的 Annotations 如下：

KeyAttribute

StringLengthAttribute

MaxLengthAttribute

ConcurrencyCheckAttribute

RequiredAttribute

TimestampAttribute

ComplexTypeAttribute

ColumnAttribute : Placed on a property to specify the column name, ordinal & data type

TableAttribute : Placed on a class to specify the table name and schema

InversePropertyAttribute : Placed on a navigation property to specify the property that represents the other end of a relationship

ForeignKeyAttribute : Placed on a navigation property to specify the property that represents the foreign key of the relationship

DatabaseGeneratedAttribute : Placed on a property to specify how the database generates a value for the property (Identity, Computed or None)

NotMappedAttribute : Placed on a property or class to exclude it from the database

8、Fluent API

View Code

//引用命名空间
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Data.Entity.Infrastructure;

namespace EFTest
{
    public class EFTestContext : DbContext
    {
        public EFTestContext()
            : base("EFTestContext") // 配置文件中连接字符串 Key 值，不写默认为类名（EFTestContext）
        {
        }

        public DbSet<Category> Categories { set; get; }
        public DbSet<Product> Products { set; get; }
        public DbSet<Supplier> Suppliers { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            //移除复数表名的契约
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
            //防止黑幕交易要不然每次都要访问 EdmMetadata这个表
            modelBuilder.Conventions.Remove<IncludeMetadataConvention>();

            modelBuilder.Entity<Supplier>()
              .Property(s => s.Name)
              .IsRequired();
        }
    }

9、附加

操作存储过程或SQL语句：

View Code

        static void Main(string[] args)
        {
            using (var db = new EFTestContext())
            {
                //执行存储过程（含有参数，如无参数，去掉最后的参数）
                int recordsAffected = db.Database.ExecuteSqlCommand("sp_DeleteProductById @id", new SqlParameter("@id", 1));
                //执行SQL语句
                string sql = string.Format("INSERT INTO [dbo].[Product] VALUES ('测试','A003')");
                recordsAffected = db.Database.ExecuteSqlCommand(sql);
            }

注解：

View Code

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

namespace EFTest
{
    //自定义表名
    [Table("MyPerson")]
    public class Person
    {
        //主键，默认情况下属性被命名为ID、id或者[ClassName]Id
        [Key]
        public int Id { set; get; }

        //设置字段不能为空
        [Required]
        public string Name { set; get; }

        //设置字段的长度范围
        [MaxLength(20),MinLength(5)]
        public string ClassName { set; get; }

        //不会创建的数据表字段
        [NotMapped]
        public int MyProperty { set; get; }

        [Column("PersonPhoto",TypeName="image")]
        public byte[] Image { set; get; }
    }

谢谢。。。