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标题: 分享一个EF 动态Lambda表达式查询类 [打印本页]

作者: 盼月亮 时间: 2015-1-10 11:18
标题: 分享一个EF 动态Lambda表达式查询类
本帖最后由盼月亮于 2015-1-10 13:44 编辑

[attach]7066[/attach][attach]7064[/attach][attach]7065[/attach]
自己用的EF动态查询，下拉框的条件是保存在数据库的，通过该类生成动态表达式查询。

/// <summary>
/// 查询表达式
/// </summary>
public static class SearchExpression
{
      private static Expression ConditonToExpression(SearchCondition condition, Expression parameter, Type type)
      {
         Expression expr = null;
         PropertyInfo pi = type.GetProperty(condition.Field);
         Expression left = Expression.Property(parameter, pi);
         object value = Convert.ChangeType(condition.Value, pi.PropertyType);//修改红色部分可支持多表（稍微思考就知道答案了，聪明的网友你想出来了吗？），上图已实现
         Expression right = Expression.Constant(value);
         switch (condition.Operator)
         {
            case "=":
                  expr = Expression.Equal(left, right);
                  break;
            case "<":
                  expr = Expression.LessThan(left, right);
                  break;
            case "<=":
                  expr = Expression.LessThanOrEqual(left, right);
                  break;
            case ">":
                  expr = Expression.GreaterThan(left, right);
                  break;
            case ">=":
                  expr = Expression.GreaterThanOrEqual(left, right);
                  break;
            case "!=":
                  expr = Expression.NotEqual(left, right);
                  break;
         }
         return expr;
      }
      /// <summary>
      /// 按条件查询
      /// </summary>
      /// <typeparam name="T">实体模型</typeparam>
      /// <param name="conditions">过滤条件</param>
      /// <returns>表达式</returns>
      public static Expression<Func<T, bool>> FindByGroup<T>(List<SearchCondition> conditions)
      {
         ParameterExpression parameter = Expression.Parameter(typeof(T), "r");
         Expression body = null;
         Type type = typeof(T);
         if (conditions.Count > 0)
         {
            body = ConditonToExpression(conditions[0], parameter, type);
            for (int i = 1; i < conditions.Count; i++)
            {
                  Expression right = ConditonToExpression(conditions, parameter, type);
                  body = conditions[i - 1].Relation.ToUpper().Equals("AND") ?
                     Expression.And(body, right) :
                     Expression.Or(body, right);
            }
         }
         if (body != null)
         {
            Expression<Func<T, bool>> expr = Expression.
                  Lambda<Func<T, bool>>(body, parameter);
            return expr;
         }
         return null;
      }
}

作者: zy32002 时间: 2015-1-10 12:33
{:soso_e179:}

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