【EF学习笔记04】----------EF简单增删改查

第一步：创建上下文对象

using(var db = new Entities())
{
    //数据操作
}

新增

    UserInfo user = new UserInfo()
    {
        UserName = "zhangsan1",
        UserPass = ""
    };
    db.UserInfo.Add(user);

删除

    user = new UserInfo()
    {
        UserID = , //根据主键删除
        UserName = "zhangsan",
        UserPass = ""
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Deleted;

说明：此例中虽然指定了UserName和UserPass属性值，但是EF执行的时候只会根据主键UserID生成查询条件，所以只需要制定UserID即可。

删除 方法2

    user = new UserInfo()
    {
        UserID =  //根据主键删除
    };
    //Attach的实体事先不能已经在内存中,否则上下文会追踪到两个相同键名的实体
    db.UserInfo.Attach(user);//将对象添加到EF管理容器中 ObjectStateManager
    db.UserInfo.Remove(user);//将对象包装类状态标识为删除

删除 先查询-再删除

    //先加载整个实体 再删除 执行了2次sql 效率略低
    using (var db = new Entities())
    {
        var user = (from v in db.UserInfo
                    where v.UserID ==
                    select v).Single();
        db.UserInfo.Remove(user);
        db.SaveChanges();
    }

修改

    user = new UserInfo()
    {
        UserID = ,
        UserName = "zhangsan",
        UserPass = ""
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Modified;

修改单个属性

    user = new UserInfo()
    {
        UserID = ,
        UserName = "zhangsan"
    };
    db.UserInfo.Attach(user);
    db.Entry<UserInfo>(user).Property<string>(v => v.UserName).IsModified = true;

说明：将UserID=12的用户名称改为 zhangsan

修改单个实体 先查询-再修改

    using (var db = new Entities())
    {
        var user = (from v in db.UserInfo
                    where v.UserName == "zhangsan"
                    select v).Single();
        user.UserPass = "123456";
        db.SaveChanges();
    }

说明：将用户名为 zhangsan的用户 密码修改为：123456

查询所有实体

    var users = db.UserInfo;
    foreach (var v in users)
    {
        ObjectDumper.Write(v);//打印实体
    }

查询单个实体 主键查询

    using (var db = new Entities())
    {
        var user = db.UserInfo.Find();
        ObjectDumper.Write(user);
    }

说明：查询UserID=12的用户

备注：所有增删改操作都需要调用 db.SaveChanges() 方法，才能更新到数据库。

完整案例：

using(var db = new Entities())
{
    //新增
    UserInfo user = new UserInfo()
    {
        UserName = "zhangsan1",
        UserPass = ""
    };
    db.UserInfo.Add(user);

    //删除
    user = new UserInfo()
    {
        UserID = , //根据主键删除
        UserName = "zhangsan",
        UserPass = ""
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Deleted;

    //删除 方法2
    user = new UserInfo()
    {
        UserID =  //根据主键删除
    };
    //Attach的实体事先不能已经在内存中,否则上下文会追踪到两个相同键名的实体
    db.UserInfo.Attach(user);//将对象添加到EF管理容器中 ObjectStateManager
    db.UserInfo.Remove(user);//将对象包装类状态标识为删除

    //删除单个实体
    //先加载整个实体 再删除 执行了2次sql 效率略低
    user = (from v in db.UserInfo
                where v.UserID ==
                select v).Single();
    db.UserInfo.Remove(user);
    db.SaveChanges();

    //修改
    user = new UserInfo()
    {
        UserID = ,
        UserName = "zhangsan",
        UserPass = ""
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Modified;

    //修改单个属性
    db.UserInfo.Attach(user);
    db.Entry<UserInfo>(user).Property<string>(v => v.UserName).IsModified = true;

    //修改单个实体
    user = (from v in db.UserInfo
                where v.UserName == "zhangsan"
                select v).Single();
    user.UserPass = "abcd";
    db.SaveChanges();

    //查询遍历
    var users = db.UserInfo;
    foreach (var v in users)
    {
        ObjectDumper.Write(v);
    }

    //查询单个实体
    user = db.UserInfo.Find();
    ObjectDumper.Write(user);

    //保存更新到数据库
    db.SaveChanges();
}