Entity Framework:代码优先

一、代码优先Code First

EF6支持Oracle ODT 12C Release 3 (net4.5)

DataModel(类)——》生成数据库DB

或

存在的数据库DB——》生成的数据模型（类）

二、创建或生成Model代码

（可利用Entity FrameWork Power Tools 生成Model代码）

先安装EFTools6.1ForVS2012 ,EF6.1版以上用EntityFramework.CodeTeplates.Csharp及自带的模板。

方式1、使用标注

/// <summary>
    /// 景点类
    /// </summary>
    [Table("DESTINATIONS", Schema = "PAMS")]
    public class Destination
    {
        [Column("DESTINATIONID", TypeName = "INT")]
        [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
        public int DestinationId { get; set; }

        [Column("NAME")]
        public string Name { get; set; }

        [Column("COUNTRY")]
        public string Country { get; set; }

        [Column("DESCRIPTION")]
        public string Description { get; set; }

        [Column("PHOTO")]
        public byte[] Photo { get; set; }

        public virtual List<Lodging> Lodgings { get; set; }
    }

    /// <summary>
    /// 住宿类
    /// </summary>
    [Table("LODGINGS", Schema = "PAMS")]
    public class Lodging
    {
        [Column("LODGINGID", TypeName = "INT")]
        [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
        public int LodgingId { get; set; }

        [Column("NAME")]
        public string Name { get; set; }

        [Column("OWNER")]
        public string Owner { get; set; }

        [Column("TARDESTINATIONID", TypeName = "INT")]
        public int? DestinationID { get; set; }

        [ForeignKey("DestinationID")]
        public Destination Destination { get; set; }
    }

    /// <summary>
    /// 度假村类
    /// </summary>
    public class Resort : Lodging
    {
        [Column("ENTERTAINMENT")]
        public string Entertainment { get; set; }
    }

    /// <summary>
    /// 宿舍类
    /// </summary>
    public class Hostel : Lodging
    {
        [Column("MAXROOM", TypeName = "INT")]
        public int? MaxRoom { get; set; }
}

方式2：使用模板Builder

public class BreakAwayContext : DbContext
{
    public DbSet<CodeFirst.Model.Destination> Destinations { get; set; }
    public DbSet<CodeFirst.Model.Lodging> Lodgings { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new DestinationMap());
        modelBuilder.Configurations.Add(new LodgingMap());
    }
}
public class DestinationMap : EntityTypeConfiguration<CodeFirst.Model.Destination>
{
    public DestinationMap()
    {
        this.HasKey(t => t.DestinationId);
        Property(d => d.Name).IsRequired();
        Property(d => d.Description).HasMaxLength();
    }

}
public class LodgingMap : EntityTypeConfiguration<CodeFirst.Model.Lodging>
{
    public LodgingMap()
    {
        this.HasKey(t => t.LodgingId);
        Property(d => d.Name).IsRequired();
        Property(d => d.Owner).HasMaxLength();
        this.Map<Lodging>(d => d.Requires("TYPE").HasValue("Standard"));
        this.Map<Resort>(d => d.Requires("TYPE").HasValue("Resort"));
        this.Map<Hostel>(d => d.Requires("TYPE").HasValue("Hostel"));
    }
}

三、配置文件

<connectionStrings>
    <add name=”BreakAwayContext ”, conectionstring=”” providerName=””>
</connectionStrings>

四、操作

1、添加

var destination = new CodeFirst.Model.Destination
{
    Country = "Indonesia",
    Description = "EcoTourism at its best in exquisite Bali",
    Name = "Bali"
};
using (var context = new CodeFirst.DataAccess.BreakAwayContext())
{
    if (context.Destinations.Count((t => t.Name == "Bali") < )
    {
        context.Destinations.Add(destination);
        context.SaveChanges();
    }
}

2、修改

using (var context = new CodeFirst.DataAccess.BreakAwayContext())
{
    var canyon = (from d in context.Destinations where d.Name == "Bali" select d).Single();
    canyon.Description = "227 mile long canyon.";

    context.Entry(gw)=EntityState.Modified;
    context.SaveChanges();
}

3、删除

using (var context = new CodeFirst.DataAccess.BreakAwayContext())
{
    //var toDelete = new CodeFirst.Model.Destination { d.Name="Bali"};
    //context.Destinations.Attach(toDelete);  //attach，状态由added改为unchanged
    //context.Destinations.Remove(toDelete);
    //context.SaveChanges();

    context.Database.ExecuteSqlCommand("delete from pams.DESTINATIONS where Name='Bali'");//直接执行sql，

}

五、查询

1、Load方法把数据加载到内存（LINQ写法，同foreach）

using (var context = new CodeFirst.DataAccess.BreakAwayContext())
{
    var query = from d in context.Destinations where d.Country == "Australia" select d;
    query.Load();//    foreach 也可以
    var count = context.Destinations.Local.Count;
}

2、ToList（）一次性从数据库中查出数据

var Invoices=ctx.Invoie.ToList();
foreach(var result in Onvoices)
{.}

3、Find方法根据键值先从内存中查询，内存中没有才查询数据库。

var destination = context.Destinations.Find();

4、Single(),SingleOrDefault(),First()等可根据条件直接从数据库查。

var destination = context.Destinations.SingleOrDefault(d => d.Name == "Bali");

六、直接执行SQL语句

1、context.Database.ExecuteSqlCommand("delete from pams.DESTINATIONS where Name='Bali'");//直接执行sql，

2、 IEnumerable<Lodging> a=context.Database.SqlQuery(“Select * from ..”) 可直接转为定义的实体类型，任何类型，EF不跟踪

3、DbSqlQuery<Lodging> c=context.Lodging.SqlQuery(“select* from ..) EF跟踪返回的对象。

4、modelBuilder.Entity<singleEntity>().HasEntitySetName(“MyEntity”) 创建实体集不需要在DBContext中定义

IEnumerable<Lodging> a=（Context as IObjectContextAdapter）.ObjectContext.CreateQuery<Lodging>(“select * from ..”) 这以后的linq查询条件可合并为一个SQL