Question

我正在尝试编写一个包含多个when子句的案例;像这样的东西：

...
case
    when 'starks' then 1
    when 'wildlings' then 2
    when 'lannisters' then 3
    Else 0
End
...

我之前用

之类的东西完成了一个条件

.OrderBy(Projections.Conditional(
    Restrictions.Where<House>(r => r.Name.IsLike("starks")),
    Projections.Constant(0),
    Projections.Constant(1))).Asc();

但我无法弄清楚如何在其中添加额外的条件/ when子句：/ 我已尝试添加额外的外部条件，额外限制等，但最终会出现语法错误..

感谢您的帮助。

Answer 1

Projections.Conditional返回IProjection，其签名为：

/// <summary>
/// Conditionally return the true or false part, dependention on the criterion
/// </summary>
/// <param name="criterion">The criterion.</param><param name="whenTrue">The when true.
///    </param><param name="whenFalse">The when false.</param>
/// <returns/>
public static IProjection Conditional(ICriterion criterion
                                    , IProjection whenTrue
                                    , IProjection whenFalse);

这意味着，第三个参数可以再次成为此条件投影：

.OrderBy
(
    Projections.Conditional(
        Restrictions.Where<House>(r => r.Name.IsLike("starks")),
        Projections.Constant(1),
        Projections.Conditional(
            Restrictions.Where<House>(r => r.Name.IsLike("wildlings")),
            Projections.Constant(2),
            Projections.Conditional(
                Restrictions.Where<House>(r => r.Name.IsLike("lannisters")),
                Projections.Constant(3),
                Projections.Constant(0)
                )
            )
        )
)
.Asc()

生成的SQL将如下所示：

ORDER BY 
(case when this_.Name LIKE 'starks'     then 1 else 
(case when this_.Name LIKE 'wildlings'  then 2 else 
(case when this_.Name LIKE 'lannisters' then 3 else 0 end) end) end) asc

在Projection.Conditionals中添加多个条件以进行查询

1 个答案: