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; } }View Code
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(); }View Code
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(); }View Code
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(); }View Code
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(); } }View Code
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);
原标题：一步步实现自己的ORM（二）
关键词：
我知道了 