Question

如何在Linq中编写以下SQL：

SELECT clientID, businessName 
  FROM clients 
  WHERE (regionID = CASE WHEN '{0}' = -1 THEN regionID ELSE '{0}' END)
  ORDER BY businessName

这是我到目前为止所做的，但我不知道如何翻译where case语句：

var result = context.clients
    .OrderBy(x => x.businessName)
    .Select(x => new
        {
            x.clientID, x.businessName, x.active, x.regionID
        })
    .OrderBy(x=> x.businessName);

Answer 1

尝试在查询中使用三元语句。我不确定它是否转换为SQL中的case语句，但你可以使用LINQPad来查找。

假设'val'包含将为{0} ...

插入的值

var result = context.clients
    .OrderBy(x => x.businessName)
    .Select(x => new
        {
            x.clientID, 
            x.businessName, 
            x.active, 
            x.regionID == -1 ? val : x.regionID
        })
    .OrderBy(x=> x.businessName);

Answer 2

假设您的变量被称为参数，您可以添加类似

的部分

 .Where(a=>a.RegionID == ((parameter == -1) ? a.RegionID : parameter));

还有另一种方法可以通过构建像

这样的查询来避免使用case语句

var query = context.clients.AsQueryable();

if (parameter != -1)
    query = query.Where(a=>a.regionID == parameter);


var result = query
    .OrderBy(x => x.Name )
    .Select(x => new
    {
       x.clientID, x.businessName
    });

如果参数为-1，则会产生类似

的内容

SELECT clientID, businessName 
FROM clients 
ORDER BY businessName

否则会生成类似

的内容

SELECT clientID, businessName 
FROM clients 
WHERE (regionID = parameter)
ORDER BY businessName

SQL to Linq Where Case Statement

2 个答案: