/// <summary>
/// 查询指定字段名并返回当前语句
/// </summary>
/// <typeparam name="T">实体类类型</typeparam>
/// <param name="cmd">查询语句</param>
/// <param name="expr">实体类属性</param>
/// <exception cref="ExpressionInvalidException">表达式不正确</exception>
/// <exception cref="NullAttributeException">没有设置特性</exception>
/// <returns>当前语句</returns>
/// <example>
/// <code lang="C#">
/// <![CDATA[
/// public class UserRepository : DatabaseTable<User>
/// {
/// //other necessary code
///
/// public User GetEntity(Int32 userID)
/// {
/// return this.Select()
/// .Querys<User>(c => new { c.UserID, c.UserName })
/// .Where<User>(c => c.UserID == userID)
/// .ToEntity<User>(this) > 0;
///
/// //SELECT UserID, UserName From tbl_Users WHERE UserID = @UserID
/// //@UserID = userID
/// }
/// }
/// ]]>
/// </code>
/// </example>
public static SelectCommand Querys <T>(this SelectCommand cmd, Expression <Func <T, Object> > expr)
{
NewExpression left = expr.Body as NewExpression;
if (left == null)
{
throw new ExpressionInvalidException();
}
foreach (MemberExpression member in left.Arguments)
{
DatabaseColumnAttribute attr = ExpressionHelper.GetColumnAttribute(cmd, member);
if (attr == null)
{
continue;
}
cmd.Query(attr.ColumnName);
}
return(cmd);
}
/// <summary>
/// 查询指定字段名并返回当前语句
/// </summary>
/// <typeparam name="T">实体类类型</typeparam>
/// <param name="cmd">查询语句</param>
/// <param name="expr">实体类属性</param>
/// <param name="function">合计函数类型</param>
/// <param name="aliasesName">字段名的别名</param>
/// <exception cref="ExpressionInvalidException">表达式不正确</exception>
/// <exception cref="NullAttributeException">没有设置特性</exception>
/// <returns>当前语句</returns>
/// <example>
/// <code lang="C#">
/// <![CDATA[
/// public class UserRepository : DatabaseTable<User>
/// {
/// //other necessary code
///
/// public Int32 Count()
/// {
/// return this.Select()
/// .Query<User>(c => c.UserID, SqlAggregateFunction.Count, "UserCount")
/// .Result<Int32>();
///
/// //SELECT COUNT(UserID) AS UserCount From tbl_Users
/// }
/// }
/// ]]>
/// </code>
/// </example>
public static SelectCommand Query <T>(this SelectCommand cmd, Expression <Func <T, Object> > expr, SqlAggregateFunction function, String aliasesName)
{
DatabaseColumnAttribute attr = SelectCommandExtension.GetColumnAttribute(cmd, expr.Body);
return(cmd.Query(function, attr.ColumnName, aliasesName));
}
