该查询如何转换为动态 Linq 表达式？答案

【问题标题】：How would this query translate into a dynamic Linq expression?该查询如何转换为动态 Linq 表达式？
【发布时间】：2012-01-23 20:34:31
【问题描述】：

select *
    from bis.CompanyInfo ci
    where ci.IsDeleted = 0
        and ci.IsBindingApproved = 1
        and ((ci.[Name] like N'%blah%'
            or ci.CityName like N'%blah%')
            or (ci.[Name] like N'%groupe%'
                or ci.CityName like N'%groupe%'))

考虑到“blah”和“groupe”是我必须搜索的关键字。要搜索的关键字数量是可变的，这就是它需要动态的地方。因此，我可以查找从 0 到数百个任意数量的关键字。

感谢任何帮助！ =)

【问题讨论】：

标签： .net linq search dynamic

【解决方案1】：

var result = (from oCompanyInfo as CompanyInfo in CompanyInfoList
             where oCompanyInfo.IsDeleted = 0 and oCompanyInfo.IsBindingApproved = 1 and             
             (Name.Contains("blah") or oCompanyInfo.CityName.Contains("blah") or
             oCompany.Name.Contains("groupe") or oCompany.CityName.Contains("groupe"))
             select oCompanyInfo).ToList()

您可以在此处将“blah”或“groupe”替换为 txtCompanyName.Text 和 txtCityName.text（如果过滤器文本在文本框中）

【讨论】：

感谢您有兴趣帮助我！ =）除此之外，我仍然遇到同样的问题，这个 Linq 查询将只接受两个且只接受两个和强制性的两个关键字。我将无法为它提供多于或少于两个关键字。这就是我希望避免并使其充满活力的。 =)

【解决方案2】：

似乎有一个命令或类似的东西加入内部过滤器。让我们将此代码作为我的 CreateFilter 方法的初始代码。

private Expression<Func<CompanyInfo, bool>> 
    CreateFilter(SearchCriterion criterion) {
    var outerFilter = PredicateBuilder.True<CompanyInfo>();
    outerFilter = outerFilter.And(ci => !ci.IsDeleted && ci.IsBindingApproved);

    var innerFilter = PredicateBuilder.False<CompanyInfo>();
    foreach(var keyword in criterion.Keywords) {
        var w = keyword;
        innerFilter = innerFilter.Or(ci => ci.Name.Contains(w)
                                        || ci.CityName.Contains(w))
    }
    outerFilter = outerFilter.And(innerFilter);

    if (criterion.HasCityName)
        outerFilter = outerFilter.And(ci => 
            ci.CityName.Contains(criterion.CityName));

    // Other similar filter here...

    return outerFilter;
}

这没有返回正确的结果。然后，根据这篇文章：LINQ: Complicated Advanced Search with Dynamic Where Clause，我更改了我的代码。

private Expression<Func<CompanyInfo, bool>> 
    CreateFilter(SearchCriterion criterion) {
    var innerFilter = PredicateBuilder.False<CompanyInfo>();
    foreach(var keyword in criterion.Keywords) {
        var w = keyword;
        innerFilter = innerFilter.Or(ci => ci.Name.Contains(w)
                                        || ci.CityName.Contains(w))
    }
    var outerFilter = PredicateBuilder.True<CompanyInfo>();
    outerFilter = outerFilter.And(ci => !ci.IsDeleted && ci.IsBindingApproved);

    if (criterion.HasCityName)
        outerFilter = outerFilter.And(ci => 
            ci.CityName.Contains(criterion.CityName));

    // Other similar filter here...

    // Here, we want to include the filter on keywords only when there are 
    // some provided with the search.
    // Otherwise, the result of the And(innerFilter) with no keywords
    // will always be 'false' and return no results though other criterion
    // might be met such as the CityName and whatever the others are.
    if (criterion.HasKeywords) outerFilter = outerFilter.And(innerFilter);

    return outerFilter;
}

而且它完美无瑕！我真的不明白为什么结果是完美的，只是因为过滤器的顺序会影响结果，这对我有用。

【讨论】：