C#博客随笔之八：EntityFramework初识

What is Entity Framework

Entity Framework (EF) is an object-relational mapper that enables .NET developers to work with relational data using domain-specific objects. It eliminates the need for most of the data-access code that developers usually need to write.

转自msdn    https://msdn.microsoft.com/en-us/data/ef.aspx?f=255&MSPPError=-2147217396

Entity Framework可以用来操作数据库

首先我们要从nuget获取EF

在控制台管理器中输入 Install-Package EntityFramework 即可安装最新版的EF

EF默认连接local db这里我们需要他支持mysql

首先我们需要从nuget获取Mysql.Data 和Mysql.Data.Entity

然后创建类

public class MysqlDbConfiguration : DbConfiguration
    {
        public MysqlDbConfiguration()
        {
            SetHistoryContext(
            "MySql.Data.MySqlClient", (conn, schema) => new MysqlHistoryContext(conn, schema));
        }

    }

 public class MysqlHistoryContext : HistoryContext
    {
        public MysqlHistoryContext(
          DbConnection existingConnection,
          string defaultSchema)
            : base(existingConnection, defaultSchema)
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {

            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<HistoryRow>().Property(h => h.MigrationId).HasMaxLength(100).IsRequired();
            modelBuilder.Entity<HistoryRow>().Property(h => h.ContextKey).HasMaxLength(200).IsRequired();
        }
    }

public class ExtMySqlMigrationSqlGenerator : MySqlMigrationSqlGenerator
    {
        protected override System.Data.Entity.Migrations.Sql.MigrationStatement Generate(System.Data.Entity.Migrations.Model.AddForeignKeyOperation op)
        {
            if (op.Name.Length > 64)
                op.Name = "FK__" + op.Name.Substring(op.Name.Length - 60, 60);

            var ret = base.Generate(op);

            return ret;
        }
        protected override System.Data.Entity.Migrations.Sql.MigrationStatement Generate(System.Data.Entity.Migrations.Model.RenameTableOperation op)
        {
            var str = base.Generate(op);
            str.Sql = str.Sql.Replace("dbo.", "");
            return str;
        }
        protected override System.Data.Entity.Migrations.Sql.MigrationStatement Generate(System.Data.Entity.Migrations.Model.DropForeignKeyOperation op)
        {
            var str = base.Generate(op);
            str.Sql = str.Sql.Replace("dbo.", "");
            return str;
        }
        protected override System.Data.Entity.Migrations.Sql.MigrationStatement Generate(System.Data.Entity.Migrations.Model.DropPrimaryKeyOperation op)
        {
            var str = base.Generate(op);
            str.Sql = str.Sql.Replace("dbo.", "");
            return str;
        }
        protected override System.Data.Entity.Migrations.Sql.MigrationStatement Generate(System.Data.Entity.Migrations.Model.AddPrimaryKeyOperation op)
        {
            var str = base.Generate(op);
            str.Sql = str.Sql.Replace("dbo.", "");
            return str;
        }

    }

　　这样，EF就可以支持mysql数据库了，因为微软的 SQL server实在是太臃肿了，所以我们选择了轻便的mysql。 这里我们使用的是MariaDb，是mysql的作者开发的开源数据库，跟mysql一毛一样，而且不用担心mysql被收购产生的其他影响。

EF是用来与数据库进行交互的，我们可以通过EF轻松的与数据库进行交互，而且在asp.net MVC的框架中，默认是安装EF的，可见EF还是比较受欢迎的，下一章将写怎么使用EF

活学活用，have fun。

么么么么哒