英文:
A lambda expression with statement body cannot be converted to an expression tree
问题
return _employeeRepository.Get().SingleOrDefault(employee =>{var mailPrefix = employee.LoginName.Split('@')[0];if (!string.IsNullOrEmpty(employee.LoginName)&& employee.IsActive.Value&& !string.IsNullOrEmpty(employee.AdGuid)&& string.Equals(mailPrefix, guestLoginName)){return true;}return false;});
错误：具有语句体的 Lambda 表达式无法转换为表达式树
英文:
return _employeeRepository.Get().SingleOrDefault(employee =>{var mailPrefix = employee.LoginName.Split('@')[0];if (!string.IsNullOrEmpty(employee.LoginName)&& employee.IsActive.Value&& !string.IsNullOrEmpty(employee.AdGuid)&& string.Equals(mailPrefix, guestLoginName)){return true;}return false;});
Error: A lambda expression with statement body cannot be converted to an expression tree
答案1
得分: 1
Sure, here's the translated code:
将员工的谓词逻辑分离为独立的布尔方法应该可以解决问题 - 代码的简单修改：private bool IsEmployeeLoginNameValid(Employee employee){var mailPrefix = employee.LoginName.Split('@')[0];if (!string.IsNullOrEmpty(employee.LoginName)&& employee.IsActive.Value&& !string.IsNullOrEmpty(employee.AdGuid)&& string.Equals(mailPrefix, guestLoginName)){return true;}return false;}然后只需这样使用它：return _employeeRepository.Get().SingleOrDefault(IsEmployeeLoginNameValid);或者return _employeeRepository.Get().SingleOrDefault(employee => IsEmployeeLoginNameValid(employee));编辑：如果你的 .Get() 返回 IQueryable，你将不得不先实例化集合以使我的建议起作用 - 否则可能会抛出错误 - 我猜你正在使用 EF 和标准查询通过仓储将 LINQ 转换为本地 SQL 查询。因此，任何本地方法/表达式都不会起作用，因为查询提供程序将无法将其转换为 SQL 查询。
英文:
Separating your predicate logic for the employee to standalone bool method should work - a simple modification of the code:
private bool IsEmployeeLoginNameValid(Employee employee){var mailPrefix = employee.LoginName.Split('@')[0];if (!string.IsNullOrEmpty(employee.LoginName)&& employee.IsActive.Value&& !string.IsNullOrEmpty(employee.AdGuid)&& string.Equals(mailPrefix, guestLoginName)){return true;}return false;}
Then just use it like this:
return _employeeRepository.Get().SingleOrDefault(IsEmployeeLoginNameValid);
Or
return _employeeRepository.Get().SingleOrDefault(employee => IsEmployeeLoginNameValid(employee));
EDIT: If you .Get() return IQueryable, you will have to materialize the collection first in order to make my suggestion work - otherwise it could throw an error -> I guess you are using EF and standard queries via repository translates the LINQ to native SQL query. So any local method/expression will not work because the query provider will not be able to transform it to sql query.
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