Linq其中条款“与”或“或”

如何解决Linq其中条款“与”或“或”

只要我有这段代码，就想知道如何使用Linq。

private IQueryable<viewTable> BaseQuery(Models.TestDataContext db)
{
   IQueryable<viewTable> query = db.viewTables;

   foreach (string row in gridCompany.GridView.GetSelectedFieldValues("CompanyCode"))
        query = query.Where(t => t.Comp_Code == row.ToString());

   return query;
}

此代码返回查询

SELECT [t0].[Column]
FROM [dbo].[viewTable] AS [t0]
WHERE ([t0].[CompanyCode] = 'ALPHA') **AND** ([t0].[CompanyCode] = 'BETA')
ORDER BY [t0].[EditDate] DESC

如何实现查询结果

SELECT [t0].[Column]
FROM [dbo].[viewTable] AS [t0]
WHERE ([t0].[CompanyCode] = 'ALPHA') **OR** ([t0].[CompanyCode] = 'BETA')
ORDER BY [t0].[EditDate] DESC

谢谢。

解决方法

如果我正确理解了您的要求，那么您想使用IN clause而不是OR运算符

SELECT [t0].[Column]
FROM [dbo].[viewTable] AS [t0]
WHERE ([t0].[CompanyCode] IN ('ALPHA','BETA')
ORDER BY [t0].[EditDate] DESC

这可以通过以下Linq2Entities查询来实现：
（我假设您正在使用ASPxGridView。）

private IQueryable<viewTable> BaseQuery(Models.TestDataContext db)
{
    var companyCodes = gridCompany.GridView.GetSelectedFieldValues("CompanyCode")
        .Select(row => row.ToString())
        .ToList();

    return db.viewTables.Where(t => companyCodes.Contains(t.Comp_Code));
}

,

使用LINQKit，您可以创建扩展方法，以对作为LINQ到数据库的过滤器的集合进行常规测试：

public static class LinqKitExt { // using LINQKit
#region Predicates
    // searchTerms - IEnumerable<TSearch> where one must match for a row
    // testFne(row,searchTerm) - test one of searchTerms against a row
    // r => searchTerms.All(s => testFne(r,s))
    public static Expression<Func<T,bool>> AnyIs<T,TSearch>(this IEnumerable<TSearch> searchTerms,Expression<Func<T,TSearch,bool>> testFne) {
        var pred = PredicateBuilder.New<T>();
        foreach (var s in searchTerms)
            pred = pred.Or(r => testFne.Invoke(r,s));

        return (Expression<Func<T,bool>>)pred.Expand();
    }
#endregion

#region Filters
#region row matches any of searchTerms
    // searchTerms - IEnumerable<TSearch> where one must match for a row
    // testFne(row,searchTerm) - test one of searchTerms against a row
    // dbq.Where(r => searchTerms.Any(s => testFne(r,s)))
    public static IQueryable<T> WhereAny<T,TSearch>(this IQueryable<T> dbq,IEnumerable<TSearch> searchTerms,bool>> testFne) =>
        dbq.Where(searchTerms.AnyIs(testFne));
    public static IQueryable<T> WhereAny<T,bool>> testFne,IEnumerable<TSearch> searchTerms) =>
        dbq.Where(searchTerms.AnyIs(testFne));
    public static IQueryable<T> WhereAny<T,params TSearch[] searchTerms) =>
        dbq.Where(searchTerms.AnyIs(testFne));
#endregion
#endregion
}

当然，AllAre / SplitContains / WhereAll / WhereSplitContains等都有相应的自然方法。

有了这些扩展名，您的查询将变为：

IQueryable<viewTable> query = db.viewTables.WhereAny(gridCompany.GridView.GetSelectedFieldValues("CompanyCode"),(v,s) => v == s);

注意：对于Contains有效的情况，这可能是一个更好的选择。