Is it possible in Linq-to-NHibernate to do a Join with a SelectMany within the same query?
It might look weird, but the idea would be to generate the following query:
select * from State
join (
select CityId, StateId
from State
inner join City on State.StateId=City.StateId
) as City on City.StateId = State.StateId
The reason is that we are using a repository pattern and I do not want to use 2 different repository to do my join.
In code, I have tried the following block, but I get a not supported exception
var states = Session.Query<State>();
var query = states.Join(states.SelectMany(x => x.Cities), state => state.StateId,
city => city.State.StateId, (state, city) => new {state, city});
var result = query.ToArray(); // <- Throws a not supported exception
I have tried the same thing with two repositories and it works:
var states = Session.Query<State>();
var cities = Session.Query<City>();
var query = states.Join(cities , state => state.StateId,
city => city.State.StateId, (state, city) => new {state, city});
var result = query.ToArray(); // <- This works perfectly fine
Thanks in advance!
Ah! I found out that I wasn't thinking the right way. I can do the equivalent by starting with a SelectMany, then do a select of both.
This is supported and will do the same thing as a join but even more optimized:
var states = Session.Query<State>();
var query = states.SelectMany(x => x.Cities).Select(city => new {city.State, city});
var result = query.ToArray(); // It works!
And with that, I don't even need to get a repo of City.
Related
I am using a LinqToSql-DataSource for a GridView in this way:
wsv.wsv2DataContext db = new wsv.wsv2DataContext();
e.KeyExpression = "id";
e.QueryableSource = (from mitgliedschaft in db.mitgliedschaft
join person in db.person on mitgliedschaft.person_id equals person.id
join institution in db.institution on mitgliedschaft.verein_id equals institution.id
select new
{
vorname = person.vorname,
nachname = person.nachname,
nameVerein = institution.name,
vereinid = mitgliedschaft.verein_id,
id = mitgliedschaft.id,
verbandsMitgliedsNummer = person.verbandsMitgliedsNummer,
strasse = person.strasse,
plz = person.plz,
ort = person.ort,
geburtsdatum = person.geburtsdatum,
geschlechtid = person.geschlechtid,
statusid = mitgliedschaft.statusid,
bezirk_id = mitgliedschaft.bezirk_id,
kreis_id = mitgliedschaft.kreis_id,
person_id = mitgliedschaft.person_id.Value,
deletedFlag = mitgliedschaft.deletedFlag,
stammverein = mitgliedschaft.stammVerein,
eintrittsdatum = mitgliedschaft.eintritt
}).GroupBy(p => p.person_id).Select(p => p.First());
}
Now i want to order the Selection. At first the "stammVerein"-Column of Table "mitgliedschaft" descending AND the Column "eintritt" of Table "mitgliedschaft". I have tried several ways:
wsv.wsv2DataContext db = new wsv.wsv2DataContext();
e.KeyExpression = "id";
e.QueryableSource = (from mitgliedschaft in db.mitgliedschaft
join person in db.person on mitgliedschaft.person_id equals person.id
join institution in db.institution on mitgliedschaft.verein_id equals institution.id
orderby mitgliedschaft.stammVerein descending, mitgliedschaft.eintritt
select new
{
...
}).GroupBy(p => p.person_id).Select(p => p.First());
}
AND:
wsv.wsv2DataContext db = new wsv.wsv2DataContext();
e.KeyExpression = "id";
e.QueryableSource = (from mitgliedschaft in db.mitgliedschaft
join person in db.person on mitgliedschaft.person_id equals person.id
join institution in db.institution on mitgliedschaft.verein_id equals institution.id
select new
{
...
}).GroupBy(p => p.person_id).Select(p => p.First()).OrderByDescending(stamm => stamm.stammverein).ThenBy(eintritt => eintritt.eintrittsdatum);
}
AND:
wsv.wsv2DataContext db = new wsv.wsv2DataContext();
e.KeyExpression = "id";
e.QueryableSource = (from mitgliedschaft in db.mitgliedschaft
join person in db.person on mitgliedschaft.person_id equals person.id
join institution in db.institution on mitgliedschaft.verein_id equals institution.id
select new
{
....
}).OrderByDescending(stamm => stamm.stammverein).ThenBy(eintritt => eintritt.eintrittsdatum).GroupBy(p => p.person_id).Select(p => p.First());
But nothing of this has any Effects ! I am very new in this kind of DataSource and Linq.
Can anyone help me achieving this order ?
Items within a grouped result will not retain their order. Depending on how you want to factor in the ordering, you will need to do it after the group by, and before, and/or after your First...
To accomplish this, it will be easiest if you map the relationships in EF with navigation properties rather than substituting SQL with Linq QL (joins and such)
Using the following base query:
var query = db.mitgliedschaft
.GroupBy(m => m.Person); // Group by related entity, not ID
For instance, after the group by, you will have sets of records grouped by Person. If you want the first Person with an earliest related record:
var result = query.OrderByDescending(g => g.Key.mitgliedschafts.Max(stamm => stamm.stammverein)
.ThenBy(stamm => stamm.eintritt.eintrittsdatum)
.First();
This is taking a wild guess at your schema & entity relationships, but hopefully it will help you work out something that fits. I can only guess at what eintritt is and how it relates to your entity model.
The initial query takes just your base entities that you want to group, and groups them by the related entity. The result of that grouping will be a set of Grouped mitgliedschafts with a key being the Person. To Order those groups by the person with the most recent mitgliedschafts we use an orderby on the Key's associated mitgliedschafts using the Max value for the collection given a descending order request.
The First then gives us the first grouped collection of mitgliedschafts.
Then if you want to sort the resulting list of mitgliedschafts after getting the person with the most recent one:
var result = query.OrderByDescending(g => g.Key.mitgliedschafts.Max(stamm => stamm.stammverein)
.ThenBy(stamm => stamm.eintritt.eintrittsdatum)
.First().OrderByDescending(stamm => stamm.stammverein)
.ThenBy(stamm => stamm.eintritt.eintrittsdatum)
.ToList();
The 2nd set of OrderBy clauses apply to the selected group, or the mitgliedschafts.
To compose the desired view model, Insert a Select() to build the view model from the mitgliedschafts before the ToList().
With the navigation properties this can probably be done without resorting to a group by. On a hunch, something like this should return something similar:
var query = db.Person
.OrderByDescending(p => p.mitgliedschafts.Max(stamm => stamm.stammverien))
.ThenBy(stamm => stamm.eintritt.eintrittsdatum)
.SelectMany(p => p.mitgliedschafts)
.OrderByDescending(stamm => stamm.stammverien)
.ThenBy(stamm => stamm.eintritt.eintrittsdatum)
.Select(stamm => new { ... })
.ToList();
Anyhow, hopefully that gives you some ideas on things to try if you have the navigation properties mapped or can set those up.
I'm accustomed to GroupBy() being more of an art than a science, but maybe someone can help me with a very specific problem:
Given the following code
var results = session.Query<MyClass>()
.GroupBy(c => c.OtherPersistentObject)
.Select(group => new
{
key = group.Key,
count = group.Count()
})
.ToList();
The generated query comes out like this:
/* [expression] */select
otherclass_.ID as col_0_0_,
cast(count(*) as INT) as col_1_0_,
otherclass_.ID as id1_1_,
otherclass_.START_DATE as start2_1_,
otherclass_.END_DATE as end3_1_,
otherclass_.Zone as zone9_1_
from
mytable mytable0_
left outer join
otherclass otherclass_
on mytable0_.otherID=otherclass_.ID
group by
mytable0_.otherID
which gives me the SQL error "Column 'otherclass .ID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause"
Is there a way to get the Select to do what I want?
TIA
It's a known NHibernate issue NH-3027.
As a workaround you can use last approach described in this answer (rewrite GroupBy part as sub-query). So your query can be rewritten to something like:
var results = session.Query<MyClass>()
.Where(c => c == session.Query<MyClass>().First(cs => cs.OtherPersistentObject == c.OtherPersistentObject))
.Select(x => new
{
key = x.OtherPersistentObject,
count = session.Query<MyClass>().Count(cs => cs.OtherPersistentObject == x.OtherPersistentObject)
}).ToList();
Try this:
var results = session
.Query<MyClass>()
.GroupBy(c => c.OtherPersistentObject)
.Select(group => new
{
key = group.Key.Id,
count = group.Count()
})
.ToList();
Here you can find the reason for the error.
I have a set of related tables that I am trying to return a result set for and I just can't get the syntax quite right to get the results I want.
I am trying to return a list of countries (United States being the only one expected right now) with appropriate states. The "appropriate" requirement is that I only want to return the states under the countries that are represented by one of our clients....ie....if we have 3 clients, 2 in Texas and 1 in OK, I need the query to return "United States (with only Texas and OK...not the other 48 states where we don't have clients).
I can get the query to return only the United States, but it returns ALL states, not just the ones I am after. This is an example of the query that I "want" to run....NOTE: FirstAdminDivision table = states table.
select * from Country c
inner join FirstAdminDivision f on f.CountryId = c.CountryId
where f.FirstAdminDivisionId IN
(
select f2.FirstAdminDivisionId from Company C
inner join [Address] a on a.AddressId = c.AddressId
inner join City cty on cty.CityId = a.CityId
inner join FirstAdminDivision f2 on f2.FirstAdminDivisionId = cty.FirstAdminDivisionId
)
This is the code I currently have (which is as close as I have been able to get) that returns the US only with all states. The "ids" list contains only Texas and OK like I would expect, so I think they issue lies in the where in the main select.
IQueryable<int> innerQ = base.Context.Set<FirstAdminDivision>().Where(x => x.Cities.Any(y => y.Addresses.Any(z => z.Companies.Any()))).Select(x => x.FirstAdminDivisionId);
List<int> ids = innerQ.ToList();
IQueryable<ICountryModel> q2 = base.Context.Set<Country>()
.Include(x => x.FirstAdminDivisions)
.Where(x => x.FirstAdminDivisions.Where(y => innerQ.Contains(y.FirstAdminDivisionId)).Any())
.Select(x => new CountryModel
{
Abbreviation = x.Abbreviation,
CountryId = x.CountryId,
Name = x.Name,
UrlDisplay = x.UrlDisplay,
FirstAdminDivisions = x.FirstAdminDivisions.Select(y => new FirstAdminDivisionModel
{
Abbreviation = y.Abbreviation,
Name = y.Name,
UrlDisplay = y.UrlDisplay
}).ToList()
});
Any help pointing out what I am missing/doing wrong would be greatly appreciated.
Well basically i would use your first query as the base query instead of all the countries and instead of returning a list of ints i would want it to return a list of FirstAdminDivision objects.
So in this case you would have two objects in that list OK and Texas. And in this case you also should have the country available since you say that FirstAdminDivision has the country as a property
Then from that list i would include country object so you can group those two state objects by country. And from that build your model using the key, country, and then the list of states.
Something like this:
IQueryable<ICountryModel> countriesWithStates = base.Context.Set<FirstAdminDivision>()
.Where(x => x.Cities.Any(y => y.Addresses.Any(z => z.Companies.Any())))
.Include(x => x.Country)
.GroupBy(x => x.Country, y=>y, (countryKey, states) => new { Country = countryKey, States = states.ToList() })
.Select(x => new CountryModel
{
Abbreviation = x.Country.Abbreviation,
CountryId = x.Country.CountryId,
Name = x.Country.Name,
UrlDisplay = x.Country.UrlDisplay,
FirstAdminDivisions = x.States.Select(y => new FirstAdminDivisionModel
{
Abbreviation = y.Abbreviation,
Name = y.Name,
UrlDisplay = y.UrlDisplay
}).ToList()
});
I have two linq queries as follows:
GroupNamesWithCorrespondingEffects
= new ObservableCollection<GroupNameWithCorrespondingEffect>(
from g in db.Groups
select new GroupNameWithCorrespondingEffect
{
GroupID = g.GroupID,
GroupName = g.GroupName,
CorrespondingEffect = g.Master_Effects.Effect
}
);
GroupNamesWithCorrespondingEffects
= new ObservableCollection<GroupNameWithCorrespondingEffect>
(GroupNamesWithCorrespondingEffects.
Where(u => !GetAllChildren(25).
Select(x => x.GroupID).
Contains(u.GroupID)).ToList());
Now how can I combine these two queries?
You can pass directly this to the constructor of the ObservableCollection:
from g in groups
let g = select new GroupNameWithCorrespondingEffect
{
GroupID = g.GroupID,
GroupName = g.GroupName,
CorrespondingEffect = g.Master_Effects.Effect
}
where !GetAllChildren(25)
.Select(x => x.GroupID)
.Contains(g.GroupID)
select g
I'm not sure if EF is able to compose the first and the second part (I can't remember from the top of my head if Contains is resolved in an IN clause, my EF is a bit rusty), but you were not doing that anyway, so the effect is the same as yours. If it is able to compose, then this way you are getting a more efficient execution.
If you don't mind mixing SQL-style and extension method syntax, you can do this:
GroupNamesWithCorrespondingEffects
= new ObservableCollection<GroupNameWithCorrespondingEffect>(
(from g in groups
select new GroupNameWithCorrespondingEffect
{ GroupID = g.GroupID,
GroupName = g.GroupName,
CorrespondingEffect = g.Master_Effects.Effect
})
.Where(u => !GetAllChildren(25)
.Select(x => x.GroupID)
.Contains(u.GroupID))
.ToList());
I have a small problem with multiple instances of the same object after a join to an other table. For testing I create one Store with two Products (ManyToMany-Relation). The following snippet hopefully describes my problem.
var preResult = _session.QueryOver<Store>().List(); // One store
Product productAlias = null;
var result = _session.QueryOver<Store>()
.JoinAlias(s => s.Products, () => productAlias)
.List(); // Two instances of the same store
I even think this behavior is correct but how can I prevent the multiple instances? Is it possible within the query?
Just for information why I need to make this unnecessary join: I want to extend the query according to different critirias, similar to this:
Product productAlias = null;
var query = _session.QueryOver<Store>().JoinAlias(s => s.Products, () => productAlias);
if (!string.IsNullOrWhiteSpace(criteria.ProductName))
{
query.Where(Restrictions.On(() => productAlias.Name).IsInsensitiveLike(criteria.ProductName));
}
if (criteria.ProductType != null)
{
query.Where(s => productAlias.Type == criteria.ProductType);
}
var result = query.List();
Here I ran into different problems, depending on the criterias.
Try using Transformers.DistinctRootEntity in your scenario to eliminate the cartesian product.
Product productAlias = null;
var query = _session.QueryOver<Store>()
.JoinAlias(s => s.Products, () => productAlias)
query = query.TransformUsing(Transformers.DistinctRootEntity);
var result = query.List();
Let's split solution into two queries.
Top one QueryOver<Store>() will be correctly returning just a distinct list. And what's more, by design it will support paging (Take(), Skip()).
The inner one, will be returning just a list of Store IDs, which fully meet whatever criteria...
The result SQL will look like this
SELECT ... // top one
FROM Store
WHERE StoreID IN ( SELECT StoreID ...) // inner one
Inner
Let's start with the inner select, the NHibernate detached QueryOver:
Store storeAlias = null;
Product productAlias = null;
// detached query, resulting in a set of searched StoreID
var subQuery = QueryOver.Of<Store>(() => storeAlias)
.JoinAlias((s) => s.Products, () => productAlias)
.Select((s) => s.ID); // ID projection
if (!string.IsNullOrWhiteSpace(criteria.ProductName))
{
subQuery.Where(Restrictions.On(() => productAlias.Code)
.IsInsensitiveLike(criteria.ProductName));
}
Top
Once we have filtered the Store we can use this subquery in top one
var query = session.QueryOver<Store>()
// IN clause
.Where(Subqueries.PropertyIn("ID", subQuery.DetachedCriteria))
.Skip(100)
.Take(50) // paging over already distinct resultset
;
var result = query.List<Store>();
And now we can apply whatever filter to inner query, and get list of Store IDs which do meet filter criteria... while working with top query, which is distinct...