我正在评估ServiceStack以确定它是否适用于通用REST服务器构建目的,并且我尝试扩展Northwind演示,我已在本地更新以使用ServiceStack 4.0.44。我调整的代码在Bitbucket here上,从git转储到hg,然后添加了我自己的changes。
我的代码和上游serviceStack.Examples northwind演示之间的区别是以下新增内容:
A ... / date / Route已添加到Orders的ServiceModel.Operations对象中:
namespace ServiceStack.Northwind.ServiceModel.Operations
{
...
[Route("/orders")]
[Route("/orders/date/{ByDate}")] // ADDED!
[Route("/orders/page/{Page}")]
[Route("/customers/{CustomerId}/orders")]
public class Orders
{
public int? Page { get; set; }
public DateTime? ByDate { get; set; } // ADDED!
public string CustomerId { get; set; }
}
然后这个案例的处理程序被添加到服务中,它在运行时因奇怪的LINQ失败而爆炸:variable 'o' of type 'ServiceStack.Northwind.ServiceModel.Types.Order' referenced from scope '', but it is not defined...
Source = System.Core
namespace ServiceStack.Northwind.ServiceInterface
{
public class OrdersService : Service
{
private const int PageCount = 20;
public object Get(Orders request)
{
List<Order> orders = null;
if (request.ByDate.HasValue)
{ // date provided
// broken LINQ #1 -- EXCEPTION HERE AT RUNTIME!
orders = Db.Select<Order>(order => order.Where<Order>(o => o.OrderDate.Value.Date == request.ByDate.Value.Date ));
/*
broken LINQ #2
orders =
Db.Select(
Db.From<Order>().
Where(o => (o != null) && o.OrderDate.HasValue && (request.ByDate.Value.Date == o.OrderDate.Value.Date)
)
);
*/
}
else if (request.CustomerId.IsNullOrEmpty())
{
orders = Db.Select<Order>(order => order.OrderByDescending(o => o.OrderDate))
.Skip((request.Page.GetValueOrDefault(1) - 1) * PageCount)
.Take(PageCount)
.ToList();
}
else
{
orders = Db.Select<Order>(order => order.Where(o => o.CustomerId == request.CustomerId));
}
if (orders.Count == 0)
异常表明我不知道如何编写LINQ表达式来按日期查询,或者它可能表示SQLM的ORM中存在内部错误,或整体框架中的错误,或者我我做错了什么。
当我尝试按DateTime值查询时,类似的运行时崩溃也会为Firebird提供程序重现,因此它可能是SQLite和Firebird ORMLite提供程序中的错误。
System.InvalidOperationException was unhandled by user code
HResult = -2146233079
Message = variable 'o' of type 'ServiceStack.Northwind.ServiceModel.Types.Order' referenced from scope '', but it is not defined
Source = System.Core
StackTrace:
at System.Linq.Expressions.Compiler.VariableBinder.Reference(ParameterExpression node, VariableStorageKind storage)
at System.Linq.Expressions.Compiler.VariableBinder.VisitParameter(ParameterExpression node)
at System.Linq.Expressions.ParameterExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at System.Linq.Expressions.ExpressionVisitor.VisitMember(MemberExpression node)
at System.Linq.Expressions.MemberExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at System.Linq.Expressions.ExpressionVisitor.VisitMember(MemberExpression node)
at System.Linq.Expressions.MemberExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at System.Linq.Expressions.Compiler.VariableBinder.VisitUnary(UnaryExpression node)
at System.Linq.Expressions.UnaryExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at System.Linq.Expressions.ExpressionVisitor.Visit(ReadOnlyCollection`1 nodes)
at System.Linq.Expressions.Compiler.VariableBinder.VisitLambda[T](Expression`1 node)
at System.Linq.Expressions.Expression`1.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at System.Linq.Expressions.Compiler.VariableBinder.Bind(LambdaExpression lambda)
at System.Linq.Expressions.Compiler.LambdaCompiler.Compile(LambdaExpression lambda, DebugInfoGenerator debugInfoGenerator)
at ServiceStack.OrmLite.SqlExpression`1.VisitMemberAccess(MemberExpression m)
at ServiceStack.OrmLite.SqlExpression`1.Visit(Expression exp)
at ServiceStack.OrmLite.SqlExpression`1.VisitBinary(BinaryExpression b)
at ServiceStack.OrmLite.SqlExpression`1.Visit(Expression exp)
at ServiceStack.OrmLite.SqlExpression`1.VisitBinary(BinaryExpression b)
at ServiceStack.OrmLite.SqlExpression`1.Visit(Expression exp)
at ServiceStack.OrmLite.SqlExpression`1.VisitLambda(LambdaExpression lambda)
at ServiceStack.OrmLite.SqlExpression`1.Visit(Expression exp)
at ServiceStack.OrmLite.SqlExpression`1.AppendToWhere(String condition, Expression predicate)
at ServiceStack.OrmLite.SqlExpression`1.Where(Expression`1 predicate)
at ServiceStack.Northwind.ServiceInterface.OrdersService.Get(Orders request) in C:\dev\ServiceStack.Examples\src\ServiceStack.Northwind\ServiceStack.Northwind.ServiceInterface\OrdersService.cs:line 19
at lambda_method(Closure, Object, Object)
at ServiceStack.Host.ServiceRunner`1.Execute(IRequest request, Object instance, TRequest requestDto)
InnerException:
解决方法:
如果我自己编写一个SQL where子句,它可以工作:
if (request.ByDate.HasValue)
{ // date provided
string condition = string.Format("OrderDate = '{0}'", request.ByDate.Value.Date.ToString("yyyy-MM-dd") );
orders = Db.Select<Order>(condition);
答案 0 :(得分:5)
ServiceStack当然可以通过DateTime进行查询。但在你的情况下,你试图只按日期部分查询,忽略时间(类似于date(OrderDate)= date(ByDate))。事情是 - 你用于表达的表达式(o.OrderDate.Value.Date == request.ByDate.Value.Date)可能看起来很简单,但它实际上由有时复杂的表达式树表示。 ORM将探索此表达式树并将其转换为原始sql查询。现在,表达式可以是任意复杂的,当然并非所有表达式都可以转换为sql查询。 ORM的开发人员应该明确考虑哪些表达式可能对实现有用。在这种情况下,最有可能的是,ORM的开发人员在访问DateTime实例的.Date属性时没有处理这种情况,或者由于某种原因甚至无法处理这种情况。您希望将其转换为类似date(OrderDate)sql的内容,但事实并非如此。其他ORM(实例框架作为示例)具有特殊功能,您可以在内部表达式中调用(例如:o =&gt; DbFunctions.Date(o.OrderDate)),但ServiceStack没有这样的功能用于仅限日期的比较,到目前为止据我所知。
长话短说 - 我说这不是一个错误但只是不支持的功能。当然,他们可能会处理这种情况并抛出更好的异常,但事实确实如此。
最后,按照DateTime进行查询,正如您的问题所述,只需执行以下操作:
var byDate = request.ByDate.Value.Date;
orders = Db.Select<Order>(order => order.OrderDate == byDate);