I am unable to use the Include("CITies") extension method on the db.Restaurants object.
When I use the include I get the following error:
DL.RESTAURANT does nto contain a definition for include or an extension method of include
namespace DL
{
public class DLgetRestaurants
{
DL.FVRGDataContext db = new FVRGDataContext();
public IEnumerable <RESTAURANT> getRestaurants(string cuisineName)
{
var restaurantList =
from RESTAURANT in db.RESTAURANTs.Include("CITies")
where RESTAURANT.CITies.Any(t => t.CITY_ID == 2)
orderby RESTAURANT.REST_NAME ascending
select RESTAURANT;
return restaurantList;
}
}
}
You can only use the Include on Entities that have a relation with another table. Other than that you shouldn't have an issue.
Related
I am using the repository pattern with Entity Framework as described in this article: repository pattern with Entity Framework
In the part where the GenericRepository is described (Generic Repository) there is a method which is used to get entities from the database set called Get. It has an orderBy but no groupBy. I am wondering how one might implement a groupBy in the same manner as the orderBy so that you can specify which field to group by dynamically on the entity.
What I have come up with is this:
Func<IQueryable<TEntity>, IGrouping<string, TEntity>> groupBy = null
and then in the method code it should be used something like this:
if(groupBy != null)
{
query = groupBy(query).ToList();
}
But this is not compiling since the IGrouping is not queryable. Does someone know how to point me in the right direction or has a solution to this?
Edit: The reason for doing this instead of using groupby on the returned list is for performance reasons. I want the groupby to be sent as an sql statement to the database and resolved there.
Grouping has no sense without projection. So you have to define new method which returns IEnumerable with new type.
I have added sample of such method. Also removed includeProperties because EF Core ignores Includes during grouping.
Usage sample:
_orderRepostory
.GetGrouped(e => e.UserId, g => new { UserId = g.Key, Count = g.Count()});
And implementation:
public class GenericRepository<TEntity> where TEntity : class
{
... // other code
public virtual IEnumerable<TResult> GetGrouped<TKey, TResult>(
Expression<Func<TEntity, TKey>> groupingKey,
Expression<Func<IGrouping<TKey, TEntity>, TResult>> resultSelector,
Expression<Func<TEntity, bool>>? filter = null)
{
var query = dbSet.AsQueryable();
if (filter != null)
{
query = query.Where(filter);
}
return query.GroupBy(groupingKey).Select(resultSelector);
}
}
I want to set a parameter in a named query (JPA 2.0), so my dataTable would render the respective dataSet. The parameter is obtained remotely and injected in a AbstractFacade class.
I've tried to achieve this through the code above, but it's not working.
Can someone help me?
AbstractFacade (main code):
private String prefDep;
public List<T> findByPrefDep() {
prefDep= FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("xPrefDep");
javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
cq.select(cq.from(entityClass));
return getEntityManager().createQuery(cq).setParameter("prefDep", prefDep).getResultList();
}
The Entity class (main code):
#NamedQuery(name = "Capacitacao.findByPrefDep", query = "SELECT c FROM Capacitacao c WHERE c.prefDep = :prefDep"),
The AbstractController:
public Collection<T> getItems() {
if (items == null) {
items = this.ejbFacade.findByPrefDep();
}
return items;
}
There is no exception launched, but the dataSet rendered corresponds to a findAll named query.
Thanks in advance.
Your code doesn't use your named query at all. A named query has a name, and your code doesn't use that name anywhere.
Use
getEntityManager().createNamedQuery("Capacitacao.findByPrefDep", Capacitacao.class)
.setParameter("prefDep", prefDep)
.getResultList();
You could have found that yourself by simply reading the EntityManager javadoc.
I have a function inside a class that will run a Linq to Entities query (or any type of Linq query actually), and it's gonna return 2 columns in the resultset. I would like to return an object to whoever is calling my function that will allow Intellisense to know what I have returned.
Let me explain. If I have a function like this:
public static IQueryable GetInfo(MyEntityModel oEntityModel)
{
var query =
(from t in oEntityModel.Table1
from u in t.Table2
where t.Status == true &&
u.Status == true
select new
{
t.Column1,
u.Column2
})
return query;
}
What can (should) I put instead of IQueryable so that whoever calls my GetInfo function, will get Intellisense from the resultset, and show that it has a Column1 and Column2?
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
if (linqresult.Column1 == 1)
{
foreach (var oItem in linqresult)
{
.. do stuff...
}
}
Tks
You cannot return an anonymous type from a function, they are strictly "inline" classes. When you return it, the foreach loop will only be able to interpret the result as an plain object. I guess you could use reflection to query the property names and values, however it seems much more straight forward to define a data transfer type to hold the results.
See this question, and this blog post.
So you could create a simple struct or class:
public class MyDataResult
{
public object Column1 { get; set; }
public object Column2 { get; set; }
}
Then modify your query in the function:
public static IQueryable<MyDataResult> GetInfo(MyEntityModel oEntityModel)
{
var query =
(from t in oEntityModel.Table1
from u in t.Table2
where t.Status == true &&
u.Status == true
select new MyDataResult
{
Column1 = t.Column1,
Column2 = u.Column2
})
return query;
}
Something like that should work. Note that I used "object" for the properties in MyDataResult. I don't know the types of the columns you are returning, you should use the actual types in order to get full intellisense.
You are returning a collection of anonymous types, they will be casted to objects, so when you try to iterate over them, altough they will be your objects (and they will contain your properties) at compile time they will be casted to objects:
foreach (var x in ClsLinqTeste.GetInfo(oEntityModel))
{
//x is an Object
}
You can read more about it here.
If you want to have intellisense, I suggest you create a custom class they will hold your properties and return not an anonymous type (using new {}) but object of your class (new MyClass(prop1, prop2)). You also need to change signature of your method, so it returns IQueryable<YourClass> and not just plain non-generic IQueryable.
As others have said, creating a new type to hold the two columns is usually the best option.
But if, for some reason, you don't want to do that and you are using .Net 4.0, you can use Tuple:
public static IQueryable<Tuple<Column1Type, Column2Type>>
GetInfo(MyEntityModel oEntityModel)
{
return from …
select Tuple.Create(t.Column1, u.Column2);
}
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
foreach (var oItem in linqresult)
Console.WriteLIne(oItem.Item1, oItem.Item2);
When you return your resultset AsQueryable, the app is already able to give you intellisense, however in your example, you must specify either .FirstOrDefault if you know your collection will only have a single row, or iterate over your collection to get the items from it, like so:
This is what you're doing:
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
if (linqresult.Column1 == 1)
{
..do stuff...
}
This is how you should do it:
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
foreach(var item in linqresult)
{
if (item.Column1 == 1)
{
..do stuff...
}
}
You must iterate over linqresult because when you query with link, it returns a result set, even if it just has one column. As with any collection, your data columns aren't available on the whole result set, only with individual items.
If you want to strongly typed enumerate a non-generic IEnumerable (IEnumerable.GetEnumerator() instead of IEnumerable<T>.GetEnumerator<T>()) you can use the Cast<>() extension, like so
var myquery = GetQueryable();
for (var item in myquery.Cast<MyDataType>())
{
// use item.Column1 directly and strongly typed with intellisense
}
I am using the latest Nhibernate and i have a linq query to return just 1 column. so I can't use for example IQueryable as there is no entity class - i am returning only 1 column. But return to IQueryable Non Generic version doesn't provide the ToList method
Here is the method
public IQueryable GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new
{
Group = c.Code
}).Distinct();
}
}
Of course if i do this (see below) i get the ToList method on my IQueryable
public IQueryable<Client> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c;
}
}
The problem being is that i need to do DISTINCT and use only 1 column.
Any ideas, i am at a loss
Thanks in advance
EDIT
When i look at the type that is returned via IQueryable it is
{NHibernate.Linq.NhQueryable<<>f__AnonymousType6>}
and looking under the base class of what is returned i see an exception
Expression type 10005 is not supported by this SelectClauseVisitor.
Wouldn't the following work?
public IQueryable<X> GetCode() // X = the type of Client.Code
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c.Code).Distinct();
}
}
The problem here is not just that you can't call ToList on a non-generic IQueryable, but that the entire result is untyped, so you cannot read the Code property of each element either. (This can be worked around with C# 4's dynamic type, but that's not really what you want here.)
In your case, I don't see why you really need to construct an anonymous type just to return a distinct sequence of Code values renamed as Group. Returning the field's value should be sufficient.
If you'd need to return more than just one column, you should create an explicit type, rather than using an anonymous type, so you can say
public IQueryable<ClientGroupAndSomething> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new ClientGroupAndSomething
{
Group = c.Code,
...
}).Distinct();
}
}
If I have something like:
var query = from children in _data.Children
where children.ChildId == childId
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
};
return query.FirstOrDefault();
Where I want the resultant object to be my custom model.
Can I handle the custom model instantiation in a different method, which could be reused if I had multiple linq queries that all generated a custom child model?
For example,
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild([param ??]);
return query.FirstOrDefault();
This may well be impossible, I don't know, but what would the method signature be like if it is possible?
I'm only thinking reuse for when multiple linq queries contain duplicate object initialisation code.
Thanks
It really depends on what version of LINQ you're using. If you're using LINQ to SQL, I don't believe you can call arbitrary methods in the query. The query translator wouldn't know what to do with the method call
If you're using LINQ to Objects, you're absolutely fine to do it, like this:
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild(children)
return query.FirstOrDefault();
// Elsewhere
public CustomModel.MyChild CreateMyCustomChild(OtherChild child)
{
return new CustomModel.MyChild
{
ChildId = child.ChildId,
Name = child.ChildName
};
}
(Side note: I'd call the range variable in the query "child" rather than "children" as at any one time it only represents a single child.)
If you wanted you could write "select 1" or in your case "CreateMyCustomChild(children)" since "children" is containing all your info. In your case you aren't adding a lot of info to "children", so why not "select children"?
In other words, just try it out. The return type of your value will determine over which type your LINQ enumerates.
Suppose you had a method that did the transform for you.
public static class Conversions
{
public static CustomModel.MyChild ToCustomModel(this DataModel.MyChild source)
{
return new CustomModel.MyChild()
{
ChildId = source.ChildId,
Name = source.ChildName
}
}
}
You can use such a method to do the conversion of a single item.
DataModel.MyChild myResult = getResult();
CustomModel.MyChild myConvertedResult = myResult.ToCustomModel()
Such a method can also be used in a Enumerable.Select method call.
IEnumerable<DataModel.MyChild> myQueriedResults = getResult();
IEnumerable<CustomModel.MyChild> myConvertedResults =
myQueryiedResults.Select(c => c.ToCustomModel());
While you can do with expressions, I don't think it is worth the hassle. Instead I suggest you define an extension method like:
IQueryable<CustomModel.MyChild> ToModel(this IQueryable<Child> childs)
{
return childs.Select( c=>
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
}
);
}
You can then call:
return _data.Children
.Where(c=>c.ChildId == childId)
.ToModel()
.FirstOrDefault();