Question

我想做一个linq， “当txtKeyword.Text为空时，查询将返回所有数据，否则它将返回包含txtKeyword.Text的数据。”

        var search = from a in Context.data
                     where txtKeyword.Text.Trim().Count() > 0 ? a.Name.Contains(txtKeyword.Text.Trim()) : true
                     select a;

Error:
DbExpressionBinding requires an input expression with a collection ResultType.
Parameter name: input

我怎样才能实现它？

Answer 1

查询构建器的查询表达式似乎过于复杂。

我会将这些代码分开：

var search = Context.data;
string filter = txtKeyword.Text.Trim();
if (!string.IsNullOrEmpty(filter))
    search = search.Where(a => a.Name.Contains(filter));

Answer 2

var search =     from a in Context.data
                 where string.IsNullOrWhitespace(txtKeyword.Text) 
                 || a.Name.Contains(txtKeyword.Text.Trim())
                 select a;

Answer 3

var search = from a in Context.data
             where txtKeyword.Text.Trim().Any() 
                   || a.Name.Contains(txtKeyword.Text)
             select a;

Answer 4

您可以在linq语句中对txtKeyword进行条件检查。像这样的东西

var search = string.IsNullOrEmpty(txtKeyword.Text)
            ? (from a in Context.data
                where a.Name.Contains(txtKeyword.Text.Trim())
                select a)
            : (from a in Context.data select a);

Answer 5

var searchText = txtKeyword.Text.Trim();
var returnAll = string.IsNullOrEmpty(searchText);

var search = from a in Context.data
                 where returnAll || a.Name.Contains(searchText)
                 select a;

LINQ按文字搜索

5 个答案: