二、手写ORM实现数据库插入

在利用反射插入时会映射所有字段：但是插入时有主键自增不需要指定值

因此利用特性标记主键，将主键排除掉

1.编写属性

[AttributeUsage(AttributeTargets.Property)]
    public class KeysAuthAtturbute : Attribute
    {
        public KeysAuthAtturbute() {}
    }

2.标记属性

3.查询除KeysAuthAtturbute之外的字段（排除主键）

  public static IEnumerable<PropertyInfo> PropertyInfoKeys(this Type type)
        {
            return type.GetProperties().Where(c => !c.IsDefined(typeof(KeysAuthAtturbute), true));
        }

　　

4.编写方法

insert用到了参数化拼接，防止SQL注入

例如：insert into Student

values(@Age,@Birthday,@Sex) 再给赋值

  public  bool insert<T>(T t)
        {
            Type type = typeof(T);//获取到具体实体类型
            string TableName = type.Name;
            string fileName = string.Join(",",type.PropertyInfoKeys().Select(p=>string.Format("[{0}]", p.Name)));
            string valuesName = string.Join(",", type.PropertyInfoKeys().Select(p => $"@{p.Name}"));//将参数以@Age,@Sex方式列出
            string sql = $@"INSERT INTO [{TableName}] ({fileName}) VALUES ({valuesName})";
            SqlCommand cmd = new SqlCommand(sql, conn);
            //用于赋值参数  数据库允许为空的情况下,判断是否有值，没有的话赋值为空值
            IEnumerable<SqlParameter> parameters = type.PropertyInfoKeys().Select(p =>
            new SqlParameter($"@{p.Name}", p.GetValue(t)??DBNull.Value));
            cmd.Parameters.AddRange(parameters.ToArray());
            if (conn.State == System.Data.ConnectionState.Closed)
            {
                conn.Open();
            }
            int result = cmd.ExecuteNonQuery();
            return result == 1;
        }

5.调用

 sqlserverDBhelper sqlserverD = new sqlserverDBhelper();
            sqlserverD.insert<Student>( new Student {
                Name = "lw",
                Age = 20,
                Birthday = DateTime.Now,
                Sex = "女",
            });

 

在程序中每次调用都需要拼接SQL字符串，使程序变得缓慢

因此利用泛型缓存加载

 

1.新建一个类 复制之前的代码，初始化构造函数里存放sql语句

 public class sqlhublider<T>
    {
        private static string selectsql = null;
        private static string insertsql = null;
        static sqlhublider()
        {
            Type type = typeof(T);//获取到具体类型
            string fileName = string.Join(",", type.PropertyInfoKeys().Select(p => string.Format("[{0}]", p.Name)));
            string valuesName = string.Join(",", type.PropertyInfoKeys().Select(p => $"@{p.Name}"));
            insertsql = $@"INSERT INTO [{type.Name}] ({fileName}) VALUES ({valuesName})";
 
            string filedstring = string.Join(",", type.GetProperties().Select(c => string.Format("[{0}]", c.Name)));
            selectsql = string.Format("select {0} from {1} where ID= ", filedstring, type.Name);
        }
 
        public static string Getsql(Sqltype sqltype)
        {
            switch (sqltype)
            {
                case sqlserver.Sqltype.selectsql:
                    return selectsql;
                case sqlserver.Sqltype.insertsql:
                    return insertsql;
                default:
                    throw new Exception("sqltype");
            }
        }
    }
    public enum Sqltype//枚举类型 不同类型的的SQL语句
    {
        selectsql,
        insertsql
    }

2.方法改编

 public  bool insert<T>(T t)
        {
             Type type = typeof(T);//获取到具体类型
             string sql= sqlhublider<T>.Getsql(Sqltype.insertsql);
            SqlCommand cmd = new SqlCommand(sql, conn);
            //用于赋值参数  数据库允许为空的情况下,判断是否有值，没有的话赋值为空值
            IEnumerable<SqlParameter> parameters = type.PropertyInfoKeys().Select(p =>
            new SqlParameter($"@{p.Name}", p.GetValue(t)??DBNull.Value));
            cmd.Parameters.AddRange(parameters.ToArray());
            if (conn.State == System.Data.ConnectionState.Closed)
            {
                conn.Open();
            }
            int result = cmd.ExecuteNonQuery();
            return result == 1;
        }

3.调用

 sqlserverDBhelper sqlserverD = new sqlserverDBhelper();
            sqlserverD.insert<Student>( new Student {
                Name = "lw",
                Age = 22,
                Birthday = DateTime.Now,
                Sex = "男",
            });
            sqlserverD.insert<Student>(new Student
            {
                Name = "lw",
                Age = 21,
                Birthday = DateTime.Now,
                Sex = "男",
            });

调试时发现，第二次插入直接使用了之前的SQL语句，不需要再次拼装了，使性能得到了提升。

泛型缓存原理：JIT会为不同的实体构造不同的类型副本