Question

请参阅以下代码：

而不是有这么多if else语句：

List<T> GetTs(string createBy, bool isAdmin, string departmentCode, ...)
{
    if(isAdmin)
    {
        if(!string.IsNullOrEmpty(createBy))
        {
            var query = context.table
                        .Where(x => string.compare(x.createBy, createBy, StringComparison.OrdinalIgnoreCase) == 0)
                        .ToList();
            return query;
        }
        else
        {
            var query = context.table.ToList();
            return query;
        }
    }
    else
    {
        if(!string.IsNullOrEmpty(createBy))
        {
            var query = context.table
                        .Where(x => string.compare(x.departmentCode, departmentCode, StringComparison.OrdinalIgnoreCase) == 0)
                        .Where(x => string.compare(x.createBy, createBy, StringComparison.OrdinalIgnoreCase) == 0)
                        .ToList();
            return query;
        }
        else
        {
            var query = context.table
                        .Where(x => string.compare(x.departmentCode, departmentCode, StringComparison.OrdinalIgnoreCase) == 0)
                        .ToList();
            return query;
        }
    }
}

我可以这样做吗，而不是那么多if else语句：

var query  = context.table
                .Where(x => (!isAdmin)? string.compare(x.departmentCode, departmentCode, StringComparison.OrdinalIgnoreCase) == 0) : SKIP THIS '.Where')
                .Where(x => (!string.IsNullOrEmpty(createBy))? string.compare(x.createBy, createBy, StringComparison.OrdinalIgnoreCase) == 0) : SKIP THIS '.Where')
                //...
                .ToList();

如果条件为假，如何告诉LINQ跳过.Where？可能的？

Patrick Hofman对以下评论的建议起作用：

var query  = context.table
                .Where(x => (!isAdmin)? string.compare(x.departmentCode, departmentCode, StringComparison.OrdinalIgnoreCase) == 0) : true)
                .Where(x => (!string.IsNullOrEmpty(createBy))? string.compare(x.createBy, createBy, StringComparison.OrdinalIgnoreCase) == 0) : true)
                //...
                .ToList();

Answer 1

如果我理解意图（有条件地应用谓词），那么基本上：不同的构成：

IQueryable<Whatever> query = context.Table;
if(condition1)
    query = query.Where(x => x.column1);
if(condition2)
    query = query.Where(x => x.column2);
//...etc
var list = query.ToList();

您可以将其包含在像

这样的扩展方法中

static IQueryable<T> WhereIf<T>(this IQueryable<T> query, bool condition,
        Expression<Func<T,bool>> predicate)
    => condition ? query.Where(predicate) : query;

和

var list= context.Table.WhereIf(condition1, x => x.column1)
                       .WhereIf(condition2, x => x.column2)
                       // ...
                       .ToList();

但是，我可能不会这样做，因为在很多情况下它需要构建一个不必要的附加表达式树。

如果条件为假，如何告诉LINQ跳过哪里？

1 个答案: