我正在尝试生成以下LINQ查询:
使用表达式树(似乎这是我需要在需要使用反射和运行时类型时唯一的方法)。请注意,实际代码中(见下文),AdAccountAlert实际上是通过反射和for循环动态生成的。 我的问题:我可以生成除了.Where()子句之外的所有内容。whereExpression方法调用由于不兼容的类型而失败。通常我知道在那里放什么,但Any()方法调用让我感到困惑。我已经尝试了我能想到的每种类型,但都没有成功。希望对.Where()和.ToDictionary()两个方法都能得到帮助。
以下是我目前的代码:
//Query the database for all AdAccountAlerts that haven't had notifications sent out
//Then get the entity (AdAccount) the alert pertains to, and find all accounts that
//are subscribing to alerts on that entity.
var x = dataContext.Alerts.Where(a => a.NotificationsSent == null)
.OfType<AdAccountAlert>()
.ToList()
.GroupJoin(dataContext.AlertSubscriptions,
a => new Tuple<int, string>(a.AdAccountId, typeof(AdAccount).Name),
s => new Tuple<int, string>(s.EntityId, s.EntityType),
(Alert, Subscribers) => new Tuple<AdAccountAlert, IEnumerable<AlertSubscription>> (Alert, Subscribers))
.Where(s => s.Item2.Any())
.ToDictionary(kvp => (Alert)kvp.Item1, kvp => kvp.Item2.Select(s => s.Username));
使用表达式树(似乎这是我需要在需要使用反射和运行时类型时唯一的方法)。请注意,实际代码中(见下文),AdAccountAlert实际上是通过反射和for循环动态生成的。 我的问题:我可以生成除了.Where()子句之外的所有内容。whereExpression方法调用由于不兼容的类型而失败。通常我知道在那里放什么,但Any()方法调用让我感到困惑。我已经尝试了我能想到的每种类型,但都没有成功。希望对.Where()和.ToDictionary()两个方法都能得到帮助。
以下是我目前的代码:
var alertTypes = AppDomain.CurrentDomain.GetAssemblies()
.Single(a => a.FullName.StartsWith("Alerts.Entities"))
.GetTypes()
.Where(t => typeof(Alert).IsAssignableFrom(t) && !t.IsAbstract && !t.IsInterface);
var alertSubscribers = new Dictionary<Alert, IEnumerable<string>>();
//Using tuples for joins to keep everything strongly-typed
var subscribableType = typeof(Tuple<int, string>);
var doubleTuple = Type.GetType("System.Tuple`2, mscorlib", true);
foreach (var alertType in alertTypes)
{
Type foreignKeyType = GetForeignKeyType(alertType);
if (foreignKeyType == null)
continue;
IQueryable<Alert> unnotifiedAlerts = dataContext.Alerts.Where(a => a.NotificationsSent == null);
//Generates: .OfType<alertType>()
MethodCallExpression alertsOfType = Expression.Call(typeof(Enumerable).GetMethod("OfType").MakeGenericMethod(alertType), unnotifiedAlerts.Expression);
//Generates: .ToList(), which is required for joins on Tuples
MethodCallExpression unnotifiedAlertsList = Expression.Call(typeof(Enumerable).GetMethod("ToList").MakeGenericMethod(alertType), alertsOfType);
//Generates: a => new { a.{EntityId}, EntityType = typeof(AdAccount).Name }
ParameterExpression alertParameter = Expression.Parameter(alertType, "a");
MemberExpression adAccountId = Expression.Property(alertParameter, alertType.GetProperty(alertType.GetForeignKeyId()));
NewExpression outerJoinObject = Expression.New(subscribableType.GetConstructor(new Type[] { typeof(int), typeof(string)}), adAccountId, Expression.Constant(foreignKeyType.Name));
LambdaExpression outerSelector = Expression.Lambda(outerJoinObject, alertParameter);
//Generates: s => new { s.EntityId, s.EntityType }
Type alertSubscriptionType = typeof(AlertSubscription);
ParameterExpression subscriptionParameter = Expression.Parameter(alertSubscriptionType, "s");
MemberExpression entityId = Expression.Property(subscriptionParameter, alertSubscriptionType.GetProperty("EntityId"));
MemberExpression entityType = Expression.Property(subscriptionParameter, alertSubscriptionType.GetProperty("EntityType"));
NewExpression innerJoinObject = Expression.New(subscribableType.GetConstructor(new Type[] { typeof(int), typeof(string) }), entityId, entityType);
LambdaExpression innerSelector = Expression.Lambda(innerJoinObject, subscriptionParameter);
//Generates: (Alert, Subscribers) => new Tuple<Alert, IEnumerable<AlertSubscription>>(Alert, Subscribers)
var joinResultType = doubleTuple.MakeGenericType(new Type[] { alertType, typeof(IEnumerable<AlertSubscription>) });
ParameterExpression alertTupleParameter = Expression.Parameter(alertType, "Alert");
ParameterExpression subscribersTupleParameter = Expression.Parameter(typeof(IEnumerable<AlertSubscription>), "Subscribers");
NewExpression joinResultObject = Expression.New(
joinResultType.GetConstructor(new Type[] { alertType, typeof(IEnumerable<AlertSubscription>) }),
alertTupleParameter,
subscribersTupleParameter);
LambdaExpression resultsSelector = Expression.Lambda(joinResultObject, alertTupleParameter, subscribersTupleParameter);
//Generates:
// .GroupJoin(dataContext.AlertSubscriptions,
// a => new { a.AdAccountId, typeof(AdAccount).Name },
// s => new { s.EntityId, s.EntityType },
// (Alert, Subscribers) => new Tuple<Alert, IEnumerable<AlertSubscription>>(Alert, Subscribers))
IQueryable<AlertSubscription> alertSubscriptions = dataContext.AlertSubscriptions.AsQueryable();
MethodCallExpression joinExpression = Expression.Call(typeof(Enumerable),
"GroupJoin",
new Type[]
{
alertType,
alertSubscriptions.ElementType,
outerSelector.Body.Type,
resultsSelector.ReturnType
},
unnotifiedAlertsList,
alertSubscriptions.Expression,
outerSelector,
innerSelector,
resultsSelector);
//Generates: .Where(s => s.Item2.Any())
ParameterExpression subscribersParameter = Expression.Parameter(resultsSelector.ReturnType, "s");
MemberExpression tupleSubscribers = Expression.Property(subscribersParameter, resultsSelector.ReturnType.GetProperty("Item2"));
MethodCallExpression hasSubscribers = Expression.Call(typeof(Enumerable),
"Any",
new Type[] { alertSubscriptions.ElementType },
tupleSubscribers);
LambdaExpression whereLambda = Expression.Lambda(hasSubscribers, subscriptionParameter);
MethodCallExpression whereExpression = Expression.Call(typeof(Enumerable),
"Where",
new Type[] { joinResultType },
joinExpression,
whereLambda);
.Where
子句的情况下是正确的(除了.ToDictionary
调用中的.Select
有时会返回空),那么您应该能够简单地确认所需的代码以生成等效于Enumerable.Range(0,2).Select(i=>Enumerable.Range(0,i)).Where(r=>r.Any())
的内容,然后添加一个“简单”的扩展,使.Where
子句变为r.item2.Any()
。 - Mark Hurd