在Projection.Conditionals为queryover添加多个条件 [英] Adding more than one condition in Projection.Conditionals for queryover

问题描述

我想写一个以上的在条款的情况;是这样的：

I am trying to write a case with more than one when clause; something like this:

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

我做了一个条件的东西，如

I've done a single conditional before with something like

.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添加一个额外的条件/ 时子句中有：/
我试图增加额外的外部条件，附加的限制等，但始终与语法错误。

But I can't figure out how to add an extra condition / when clause in there :/ I've tried adding an extra outer conditional, extra restriction etc, but always end up with syntax error..

感谢您的帮助。

推荐答案

的 Projections.Conditional 返回 IProjection ，它的签名是：

/// <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这个条件预测：

And that means, that the third parameter can again be this Conditional projection:

.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看起来像：

The generated SQL will look like:

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

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