一步步实现自己的ORM（二）

2019-11-14 16:07:13

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在第一篇《一步步实现自己的ORM（一）》里，我们用反射获取类名、属性和值，我们用这些信息开发了简单的INSERT方法，在上一篇文章里我们提到主键为什么没有设置成自增长类型，单单从属性里我们无法识别哪个是主键，今天我们用Attribute来标识列，关于Attribute，引用MSDN里描述

MADN的定义为：公共语言运行时允许添加类似关键字的描述声明，叫做attributes, 它对程序中的元素进行标注，如类型、字段、方法和属性等。Attributes和Microsoft .NET Framework文件的元数据（metadata）保存在一起，可以用来向运行时描述你的代码，或者在程序运行的时候影响应用程序的行为。我们简单的总结为：定制特性attribute，本质上是一个类，其为目标元素提供关联附加信息，并在运行期以反射的方式来获取附加信息。

简单来说Attribute就是描述类、方法、属性参数等信息的。

可参考《浅析C#中的Attribute》

在这里我们定义2个Attribute，用来描述表和字段。

    [AttributeUsage(AttributeTargets.Class)]    class TableAttribute : Attribute    {        /// <summary>        /// 表名        /// </summary>        public string Name { get; PRivate set; }        public TableAttribute(string name)        {            this.Name = name;        }    }    [AttributeUsage(AttributeTargets.Property)]    class ColumnAttribute : Attribute    {        /// <summary>        /// 是否为数据库自动生成        /// </summary>        public bool IsGenerated { get; set; }        /// <summary>        /// 列名        /// </summary>        public string Name { get; private set; }        public ColumnAttribute(string name)        {            this.Name = name;        }    }

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修改后的实体类如下：

    [Table("tb_Users")]    public class User    {        [Column("UserId",IsGenerated = true)]        public int UserId { get; set; }        [Column("Email")]        public string Email { get; set; }        [Column("CreatedTime")]        public DateTime CreatedTime { get; set; }    }

我们把表结构也修改下

CREATE TABLE [dbo].[tb_Users](    [UserId] [int] NOT NULL identity(1,1) PRIMARY KEY ,    [Email] [nvarchar](100) NULL,    [CreatedTime] [datetime] NULL)

下面的问题，就是我们如何得到表名和字段名呢？我们还是采用反射来实现，先获取表名：

         TableAttribute[] tableAttr = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttr.Length>0)            {                Console.WriteLine(tableAttr[0].Name);            }

运行结果

再获取列名，先查找property，然后找Attribute，代码如下：

            var properties = typeof(User).GetProperties();            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (columnAttrs.Length>0)                {                    Console.WriteLine("字段名：{0}，是否为自动生成：{1}", columnAttrs[0].Name, columnAttrs[0].IsGenerated);                }            }

运行结果

再来修改INSERT 方法如下：

public static int Insert(User user)        {            var type = typeof(User);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else {                tableName = type.Name;            }            /*将所有的列放到集合里*/            List<ColumnAttribute> columns = new List<ColumnAttribute>();            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0)                {                    columns.Add(attrs[0]);                }            }            StringBuilder sql = new StringBuilder();            sql.Append("INSERT INTO [").Append(tableName).Append("](");            int paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0 && attrs[0].IsGenerated == false)                {                    if (paramIndex > 0)                        sql.Append(",");                    sql.Append(attrs[0].Name);                    paramIndex++;                }            }            sql.Append(") VALUES (");            paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0 && attrs[0].IsGenerated == false)                {                    if (paramIndex > 0)                        sql.Append(",");                    sql.Append("@p").Append(paramIndex);                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));                    paramIndex++;                }            }            sql.Append(")");            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }

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运行结果

我们再定义一个IdAttribute 类用来表示主键，它不需要任何属性

    [AttributeUsage(AttributeTargets.Property)]    class IdAttribute :ColumnAttribute    {        public IdAttribute(string name) : base(name)        {        }    }

有了主键我们下面可以写UPDATE和DELETE 方法：

UPDATE：

  public static int Update(User user)        {            var type = typeof(User);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else            {                tableName = type.Name;            }            StringBuilder sql = new StringBuilder();            sql.Append("UPDATE [").Append(tableName).Append("] SET ");            int paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (idAttrs.Length > 0) //如果是主键 跳过                    continue;                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (columnAttrs.Length > 0)                 {                    if (paramIndex > 0)                        sql.Append(",");                    // 字段 = @p                    sql.Append(columnAttrs[0].Name).Append("=").Append("@p" + paramIndex);                    /*参数*/                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));                    paramIndex++;                }            }            sql.Append(" WHERE ");            int keyIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (idAttrs.Length > 0)                {                    if (keyIndex > 0) //考虑到有多个主键                        sql.Append(" AND ");                    sql.Append(idAttrs[0].Name).Append("=").Append("@p").Append(paramIndex);                    /*参数*/                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));                    paramIndex++;                    keyIndex++;                }            }            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }

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调用代码：

            Update(new User()            {                UserId = 1,                Email = "new@new.com",                CreatedTime = DateTime.Now            });

运行结果：

DELETE方法：

        public static int DeleteByKey(params object[] values)        {            var type = typeof(User);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else            {                tableName = type.Name;            }                        /*将所有的列放到集合里*/            List<IdAttribute> columns = new List<IdAttribute>();            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (attrs.Length > 0)                {                    columns.Add(attrs[0]);                }            }            if (columns.Count != values.Length)                throw new ArgumentException("参数个数和主键数不一致");            StringBuilder sql = new StringBuilder();            sql.Append("DELETE FROM [").Append(tableName).Append("] ").Append(" WHERE ");            for (int i = 0; i < columns.Count; i++)            {                if (i > 0) //考虑到有多个主键                    sql.Append(" AND ");                sql.Append(columns[i].Name).Append("=").Append("@p").Append(i);                /*参数*/                parameters.Add("@p" + i, values[i]);            }            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }

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调用代码：

 DeleteByKey(1);

运行结果

最后我们把增删改方法放在一个泛型类里。

    class EntityHelper    {        private const string connectionString = "";        public static int Insert<T>(T entity)        {            var type = typeof(T);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else            {                tableName = type.Name;            }            /*将所有的列放到集合里*/            List<ColumnAttribute> columns = new List<ColumnAttribute>();            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0)                {                    columns.Add(attrs[0]);                }            }            StringBuilder sql = new StringBuilder();            sql.Append("INSERT INTO [").Append(tableName).Append("](");            int paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0 && attrs[0].IsGenerated == false)                {                    if (paramIndex > 0)                        sql.Append(",");                    sql.Append(attrs[0].Name);                    paramIndex++;                }            }            sql.Append(") VALUES (");            paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (attrs.Length > 0 && attrs[0].IsGenerated == false)                {                    if (paramIndex > 0)                        sql.Append(",");                    sql.Append("@p").Append(paramIndex);                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));                    paramIndex++;                }            }            sql.Append(")");            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }        public static int Update<T>(T entity)        {            var type = typeof(T);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else            {                tableName = type.Name;            }            StringBuilder sql = new StringBuilder();            sql.Append("UPDATE [").Append(tableName).Append("] SET ");            int paramIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (idAttrs.Length > 0) //如果是主键 跳过                    continue;                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);                if (columnAttrs.Length > 0)                {                    if (paramIndex > 0)                        sql.Append(",");                    // 字段 = @p                    sql.Append(columnAttrs[0].Name).Append("=").Append("@p" + paramIndex);                    /*参数*/                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));                    paramIndex++;                }            }            sql.Append(" WHERE ");            int keyIndex = 0;            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (idAttrs.Length > 0)                {                    if (keyIndex > 0) //考虑到有多个主键                        sql.Append(" AND ");                    sql.Append(idAttrs[0].Name).Append("=").Append("@p").Append(paramIndex);                    /*参数*/                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));                    paramIndex++;                    keyIndex++;                }            }            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }        public static int DeleteByKey<T>(params object[] values)        {            var type = typeof(T);            Dictionary<string, object> parameters = new Dictionary<string, object>();            var properties = type.GetProperties();            string tableName = string.Empty;            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);            if (tableAttrs.Length > 0)            {                tableName = tableAttrs[0].Name;            }            else            {                tableName = type.Name;            }            /*将所有的列放到集合里*/            List<IdAttribute> columns = new List<IdAttribute>();            for (int i = 0; i < properties.Length; i++)            {                var pi = properties[i];                var attrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);                if (attrs.Length > 0)                {                    columns.Add(attrs[0]);                }            }            if (columns.Count != values.Length)                throw new ArgumentException("参数个数和主键数不一致");            StringBuilder sql = new StringBuilder();            sql.Append("DELETE FROM [").Append(tableName).Append("] ").Append(" WHERE ");            for (int i = 0; i < columns.Count; i++)            {                if (i > 0) //考虑到有多个主键                    sql.Append(" AND ");                sql.Append(columns[i].Name).Append("=").Append("@p").Append(i);                /*参数*/                parameters.Add("@p" + i, values[i]);            }            Console.WriteLine(sql);            SqlConnection conn = new SqlConnection(connectionString);            var cmd = conn.CreateCommand();            cmd.CommandText = sql.ToString();            foreach (var item in parameters)            {                var pa = cmd.CreateParameter();                pa.ParameterName = item.Key;                pa.Value = item.Value ?? DBNull.Value;                cmd.Parameters.Add(pa);            }            conn.Open();            return cmd.ExecuteNonQuery();        }    }

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大功告成，我们修改下调用代码

           EntityHelper.Insert(new User()            {                Email = "abc@123.com",                CreatedTime = DateTime.Now            });            EntityHelper.Update(new User()            {                UserId = 1,                Email = "new@new.com",                CreatedTime = DateTime.Now            });            EntityHelper.DeleteByKey<User>(1);