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;
}
}
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();
}
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();
}
调用代码：
Update(new User()
{
UserId = 1,
Email = "[email protected]",
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();
}
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();
}
}
大功告成，我们修改下调用代码
EntityHelper.Insert(new User()
{
Email = "[email protected]",
CreatedTime = DateTime.Now
});
EntityHelper.Update(new User()
{
UserId = 1,
Email = "[email protected]",
CreatedTime = DateTime.Now
});
EntityHelper.DeleteByKey<User>(1);
时间： 2024-08-02 06:59:59