一步步实现自己的ORM（二）

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。

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);