EF4 LINQ Включить (строку) альтернативу жестко закодированной строке?
Ответ @aaronheckmann работал для меня, но мне пришлось заменить return doc.tags.length; на return doc.tags != null;, потому что это поле содержит null, если оно не совпадает с условиями, записанными внутри заполнения. Итак, окончательный код:
query....
.exec(function(err, docs){
docs = docs.filter(function(doc){
return doc.tags != null;
})
// do stuff with docs
});
13
задан Craig Stuntz 6 April 2010 в 16:21
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3 ответа
Для Entity Framework 1.0 я создал несколько методов расширения для этого.
public static class EntityFrameworkIncludeExtension
{
public static ObjectQuery<T> Include<T>(this ObjectQuery<T> src, Expression<Func<T, StructuralObject>> fetch)
{
return src.Include(CreateFetchingStrategyDescription(fetch));
}
public static ObjectQuery<T> Include<T>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch)
{
return src.Include(CreateFetchingStrategyDescription(fetch));
}
public static ObjectQuery<T> Include<T, TFectchedCollection>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<TFectchedCollection>>> fetch)
{
return src.Include(CreateFetchingStrategyDescription(fetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, Object>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, RelatedEnd>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, RelatedEnd>> fetch, Expression<Func<FetchedChild, StructuralObject>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, Object>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, RelatedEnd>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
public static ObjectQuery<T> Include<T, FetchedChild>(this ObjectQuery<T> src, Expression<Func<T, IEnumerable<FetchedChild>>> fetch, Expression<Func<FetchedChild, StructuralObject>> secondFetch)
where FetchedChild : StructuralObject
{
return src.Include(CombineFetchingStrategies(fetch, secondFetch));
}
private static String CreateFetchingStrategyDescription<TFetchEntity, TFetchResult>(
Expression<Func<TFetchEntity, TFetchResult>> fetch)
{
fetch = (Expression<Func<TFetchEntity, TFetchResult>>)FixedWrappedMemberAcces.ForExpression(fetch);
if (fetch.Parameters.Count > 1)
throw new ArgumentException("CreateFetchingStrategyDescription support only " +
"one parameter in a dynamic expression!");
int dot = fetch.Body.ToString().IndexOf(".") + 1;
return fetch.Body.ToString().Remove(0, dot);
}
private static String CreateFetchingStrategyDescription<T>(Expression<Func<T, Object>> fetch)
{
return CreateFetchingStrategyDescription<T, Object>(fetch);
}
private static String CombineFetchingStrategies<T, TFetchedEntity>(
Expression<Func<T, Object>> fetch, Expression<Func<TFetchedEntity, Object>> secondFetch)
{
return CombineFetchingStrategies<T, Object, TFetchedEntity, Object>(fetch, secondFetch);
}
private static String CombineFetchingStrategies<TFetchEntity, TFetchResult, TFetchedEntity, TSecondFetchResult>(
Expression<Func<TFetchEntity, TFetchResult>> fetch, Expression<Func<TFetchedEntity, TSecondFetchResult>> secondFetch)
{
return CreateFetchingStrategyDescription<TFetchEntity, TFetchResult>(fetch) + "." +
CreateFetchingStrategyDescription<TFetchedEntity, TSecondFetchResult>(secondFetch);
}
}
Использование:
Orders.Include(o => o.Product); // generates .Include("Product")
Orders.Include(o => o.Product.Category); // generates .Include("Product.Category")
Orders.Include(o => o.History); // a 1-* reference => .Include("History")
// fetch all the orders, and in the orders collection.
// also include the user reference so: .Include("History.User")
// but because history is an collection you cant write o => o.History.User,
// there is an overload which accepts a second parameter to describe the fetching
// inside the collection.
Orders.Include(o => o.History, h => h.User);
Я не тестировал это на EF4.0, но надеюсь, что это сработает.
10
ответ дан 1 December 2019 в 19:30
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Это довольно просто сделать, используя Выражения:
public static class ObjectQueryExtensions
{
public static ObjectQuery<T> Include<T, TProperty>(this ObjectQuery<T> objectQuery, Expression<Func<T, TProperty>> selector)
{
MemberExpression memberExpr = selector.Body as MemberExpression;
if (memberExpr != null)
{
return objectQuery.Include(memberExpr.Member.Name);
}
throw new ArgumentException("The expression must be a MemberExpression", "selector");
}
}
Вы можете использовать это точно так же, как в примере в вашем вопросе
ОБНОВЛЕНИЕ
Улучшенная версия, которая поддерживает несколько связанных свойств:
public static class ObjectQueryExtensions
{
public static ObjectQuery<T> Include<T, TProperty>(this ObjectQuery<T> objectQuery, Expression<Func<T, TProperty>> selector)
{
string propertyPath = GetPropertyPath(selector);
return objectQuery.Include(propertyPath);
}
public static string GetPropertyPath<T, TProperty>(Expression<Func<T, TProperty>> selector)
{
StringBuilder sb = new StringBuilder();
MemberExpression memberExpr = selector.Body as MemberExpression;
while (memberExpr != null)
{
string name = memberExpr.Member.Name;
if (sb.Length > 0)
name = name + ".";
sb.Insert(0, name);
if (memberExpr.Expression is ParameterExpression)
return sb.ToString();
memberExpr = memberExpr.Expression as MemberExpression;
}
throw new ArgumentException("The expression must be a MemberExpression", "selector");
}
}
Пример:
var query = X.Include(x => x.Foo.Bar.Baz) // equivalent to X.Include("Foo.Bar.Baz")
8
ответ дан 1 December 2019 в 19:30
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