string.IsNullOrEmpty + Entity Framework 5

Question

我已经使用了Entity Framework已经有一段时间了,我正在重新使用EF 5,但不会这个查询:

SELECT 
    c.OrganizationName as CompanyName,
    c.OrganizationKey as CompanyId,
    ISNULL(a.Line1, '') as Line1,
    ISNULL(a.Line2, '') as Line2,
    a._CityStateZip as CityStateZip
FROM Organizations c
JOIN Addresses a ON c.AddressKey = a.AddressKey
WHERE c.OrganizationName LIKE @term + '%'
AND c.IsSuspended = 0
AND c.IsActive = 1

与以下相同:

var results = (from c in adms.Organizations
               where c.OrganizationName.StartsWith(term)
               where !c.IsSuspended
               where c.IsActive
               select new
               {
                 CompanyName = c.OrganizationName,
                 CompanyId = c.OrganizationKey,
                 Line1 = (string.IsNullOrEmpty(c.Address.Line1) ? string.Empty : c.Address.Line1),
                 Line2 = (string.IsNullOrEmpty(c.Address.Line2) ? string.Empty : c.Address.Line2),
                 CityStateZip = c.Address._CityStateZip
               }).ToList();

当我运行LINQ to SQL代码时,我收到以下错误:

Could not translate expression 
'Table(Organization).Where(c => c.OrganizationName
.StartsWith(Invoke(value(System.Func`1[System.String]))))
.Where(c => Not(c.IsSuspended))
.Where(c => c.IsActive)
.Select(c => new <>f__AnonymousType2`5(
CompanyName = c.OrganizationName, 
CompanyId = c.OrganizationKey, 
Line1 = IIF(IsNullOrEmpty(c.Address.Line1), 
Invoke(value(System.Func`1[System.String])), c.Address.Line1), 
Line2 = IIF(IsNullOrEmpty(c.Address.Line2), 
Invoke(value(System.Func`1[System.String])), c.Address.Line2), 
CityStateZip = c.Address._CityStateZip))' 
into SQL and could not treat it as a local expression.

我在这里完全遗漏了什么吗？我以为我可以使用string.IsNullOrEmpty和LINQ to SQL.

Answer 1

替换string.Empty为"".可悲的是,EF不支持string.Empty.

EF LINQ支持一般非常糟糕.始终要注意这个问题.这是EF的悲伤的常见原因.

LINQ to SQL没有常见语言习语的问题.

顺便说一句,你可以更好地重写这个:c.Address.Line1 ?? "".