动态表达式树如何

发布于 2024-08-25 23:45:28 字数 780 浏览 8 评论 0原文

使用多种方法实现了通用存储库。其中之一是：

public IEnumerable<T> Find(Expression<Func<T, bool>> where)
        {
            return _objectSet.Where(where);
        }

给定为，很容易这样称呼它：

Expression<Func<Culture, bool>> whereClause = c => c.CultureId > 4 ;

return cultureRepository.Find(whereClause).AsQueryable();

但现在我看到（意识到）这种查询的目的是“仅限制一个条件”。我想做的是：

在上面的例子中，c 是文化类型。文化有几个属性，例如 CultureId、Name、Displayname... 我该如何表达以下内容：文化ID> 4 和 Name.contains('de') 并在另一个执行中 Name.contains('us') 和 Displayname.contains('ca') 和 ....

这些查询应该动态创建。我查看了表达式树（因为我认为这是解决我的问题的方法 - 顺便说一句，我以前从未使用过它们），但我找不到任何符合我要求的内容。

这如何构建？

提前致谢

原文

Implemented a generic repository with several Methods. One of those is this:

public IEnumerable<T> Find(Expression<Func<T, bool>> where)
        {
            return _objectSet.Where(where);
        }

Given <T> to be <Culture> it is easy to call this like this:

Expression<Func<Culture, bool>> whereClause = c => c.CultureId > 4 ;

return cultureRepository.Find(whereClause).AsQueryable();

But now i see (realize) that this kind of quering is "limiting only to one criteria".
What i would like to do is this:

in the above example c is of type Culture. Culture has several properties like CultureId, Name, Displayname,...
How would i express the following:
CultureId > 4 and Name.contains('de') and in another execution
Name.contains('us') and Displayname.contains('ca') and ....

Those queries should be created dynamically.
I had a look in Expression trees (as i thought this to be a solution to my problem - btw i never used them before) but i cannot find anything which points to my requirement.

How can this be costructed?

Thanks in advance

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黑寡妇 2024-09-01 23:45:28

您不需要做任何特别的事情，以下内容就可以工作：

var whereClause = c => (c.CultureId > 4 && c.Name.Contains("de"));

You don't need to do anything special, the following will work:

var whereClause = c => (c.CultureId > 4 && c.Name.Contains("de"));

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潇烟暮雨 2024-09-01 23:45:28

关于对一个参数的限制，Codeka 给了我一个重新思考我的陈述的提示。

事实证明，使用我们想要查询的所有具有值的属性来实现场景非常容易。例如，如果 Cutlure 类型定义有 3 个属性

Name string

Displayname string

CultureId int

，则可以实现这样的 Filter-Expression

Expression<Func<Culture, bool>> whereClause = c => (
                (!String.IsNullOrEmpty(FilterCulture.Name) ? c.Name.Contains(FilterCulture.Name) : true) &&
                (!String.IsNullOrEmpty(FilterCulture.Displayname) ? c.Displayname.Contains(FilterCulture.Displayname) : true) &&
                (FilterCulture.CultureId > 0 ? c.CultureId == FilterCulture.CultureId : true)
                );

正如您所见，我正在使用 &&每个属性之间的运算符来缩小结果（可以使用 || 来扩大结果 - 从而实现 OR）。

再次感谢codeka！

Codeka gave me a hint for re-thinking my statement, regarding this limitation to one parameter.

Turns out it very easy to implement a scenario with all the properties we want to query, which have values. For example if the Cutlure type is defined with 3 properties

Name string

Displayname string

CultureId int

than one can implement a Filter-Expression like this

Expression<Func<Culture, bool>> whereClause = c => (
                (!String.IsNullOrEmpty(FilterCulture.Name) ? c.Name.Contains(FilterCulture.Name) : true) &&
                (!String.IsNullOrEmpty(FilterCulture.Displayname) ? c.Displayname.Contains(FilterCulture.Displayname) : true) &&
                (FilterCulture.CultureId > 0 ? c.CultureId == FilterCulture.CultureId : true)
                );

As you can see i 'm using the && operator between each property to narrow the results (one could use the || to widen the results - thus implementing OR).

Thank you again codeka !

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