I have Personne (person) entity with sub collections Polices and Procedures. I want to load a batch of Personnes with those collections loaded as well, using the power of Future queries. But! I was asked not to duplicate the columns of Personne in the queries getting the Polices and Procedures, which seems wise to optimize the amount of data traveling from database to server.
Here is what I ended up doing.
public IList<Personne> GetForDTO(IList<int> ids)
{
IEnumerable<Personne> query = NHibernateSession.Current.Query<Personne>()
.Fetch(x => x.Adresse)
.Where(x => ids.Contains(x.Id))
.ToFuture();
var queryWithPolices = NHibernateSession.Current.Query<Personne>()
.FetchMany(x => x.Polices)
.Where(x => ids.Contains(x.Id))
.Select(x => new
{
x.Id,
x.Polices
})
.ToFuture();
var queryWithProcedures = NHibernateSession.Current.Query<Personne>()
.FetchMany(x => x.Procedures)
.Where(x => ids.Contains(x.Id))
.Select(x => new
{
x.Id,
x.Procedures
})
.ToFuture();
return query.ToList();
}
This query doesn't work, with error:
Collections.IList' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable`1[System.Object]'
It does work if I remove the Select() line call, but of course it results in the Personne columns being fetched as well as the Polices and Procedures columns.
Any idea of to fix this?
change return type 'IList' to 'IEnumerable'
Change your return type to IEnumerable:
public IIEnumerable<Personne> GetForDTO(IList<int> ids)
Related
I am trying to convert the result of the query into IDictionary
Here string will contain orderId and the int will contain the TradedQuantity
The query below should join three objects Order, OrderRevision and OrderEvent.
1 Order can have many orderRevisions
1 OrderRevision can have many orderEvents
What the query is trying to do is to inner join three objects and get all order objects whose order id matches the list of orderids supplied to it. Then it does a group by based on orderId and gets the latest TradedQuantity from orderEvents object. LatestTradedQuantity will be the TradedQuantityFrom latest OrderEvent. For now the latest orderevent can be regarded as the one that has highest OrderEventId value.
OrderRevision revisionAlias = null;
Order orderAlias = null;
var query =
Session.QueryOver<OrderEvent>()
.JoinAlias(oe => oe.OrderRevision,() => revisionAlias)
.JoinAlias(oe => oe.OrderRevision.Order,() => orderAlias)
.Where(x => x.OrderRevision.Order.SourceSystem.Name.ToLower() == sourceSystem.ToLower())
.WhereRestrictionOn(x => x.OrderRevision.Order.Id).IsIn(orderIds.ToList())
.SelectList(list => list.SelectGroup(x => x.OrderRevision.Order.SourceOrderIdentifier)
.SelectMax(x => x.Id).Select(x => x.TradedQuantity))
.Select(x => new KeyValuePair<string, int?>(x.OrderRevision.Order.SourceOrderIdentifier, x.TradedQuantity)
);
As this query does not do what is supposed to. Could you please help and let me know how the result can be cast into IDictionary?
You have tagged your question with linq-to-nhibernate, so I guess using it instead of queryover would suit you. With Linq, use a sub-query for selecting the "max" order events ids for each order, then query them and project them to a dictionary.
using System.Linq;
using NHibernate.Linq;
...
var orderEventsIdsQuery = Session.Query<OrderEvent>()
.Where(oe => orderIds.Contains(oe.OrderRevision.Order.Id))
.GroupBy(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
(soi, oes) => oes.Max(oe => oe.Id));
var result = Session.Query<OrderEvent>()
.Where(oe => orderEventsIdsQuery.Contains(oe.Id))
.ToDictionary(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
oe => oe.TradedQuantity);
This should do the job. I do not use QueryOver and I will not try to give an answer for doing it with QueryOver.
this code written by #Rahul Singh in this post Convert TSQL to Linq to Entities :
var result = _dbContext.ExtensionsCategories.ToList().GroupBy(x => x.Category)
.Select(x =>
{
var files = _dbContext.FileLists.Count(f => x.Select(z => z.Extension).Contains(f.Extension));
return new
{
Category = x.Key,
TotalFileCount = files
};
});
but this code have problem when used inside database context and we should use ToList() like this to fix "Only primitive types or enumeration types are supported in this context" error :
var files = _dbContext.FileLists.Count(f => x.Select(z => z.Extension).ToList().Contains(f.Extension));
the problem of this is ToList() fetch all records and reduce performance, now i wrote my own code :
var categoriesByExtensionFileCount =
_dbContext.ExtensionsCategories.Select(
ec =>
new
{
Category = ec.Category,
TotalSize = _dbContext.FileLists.Count(w => w.Extension == ec.Extension)
});
var categoriesTOtalFileCount =
categoriesByExtensionFileCount.Select(
se =>
new
{
se.Category,
TotalCount =
categoriesByExtensionFileCount.Where(w => w.Category == se.Category).Sum(su => su.TotalSize)
}).GroupBy(x => x.Category).Select(y => y.FirstOrDefault());
the performance of this code is better but it have much line of code, any idea about improve performance of first code or reduce line of second code :D
Regards, Mojtaba
You should have a navigation property from ExtensionCategories to FileLists. If you are using DB First, and have your foreign key constraints set up in the database, it should do this automatically for you.
If you supply your table designs (or model classes), it would help a lot too.
Lastly, you can rewrite using .ToList().Contains(...) with .Any() which should solve your immediate issue. Something like:
_dbContext.FileLists.Count(f => x.Any(z => z.Extension==f.Extension)));
I am using NHibernate with mapping by code.
I have three models: Solution, Installation and System. There are one-to-many relations between them. So that each Solution has a list of Installations, and each Installation has a list of Systems.
Each system has a property "Type", which can be "1" or "0".
I am trying to write a method in the Solution repository that will return all the Solutions, with their Installations with only the Systems of type "1".
I have tried the Where-keyword in the SystemMap but i get the same result with and without it. Then i tried a few different experiments with QueryOver(???) without success.
How do i go about to filter on information in the last node?
Thank to your answer, i have done the following implementation, but it results in a huge amount of Systems and Solutions. Maybe i have done something wrong?
The Maps are as follows:
public SAPSolutionMap()
{
Id(t => t.YPID);
Property(e => e.ShortName);
Property(e => e.FullName);
Bag(x => x.SapInstallations, colmap =>
{
colmap.Table("SAPInstallation");
colmap.Key(x => x.Column("Solution"));
colmap.Inverse(true);
colmap.Lazy(CollectionLazy.NoLazy);
colmap.Fetch(CollectionFetchMode.Join);
colmap.Cascade(Cascade.None);
}, map => map.OneToMany(m => m.Class(typeof(SAPInstallation))));
}
public SAPInstallationMap()
{
Id(t => t.InstallationNumber);
Bag(x => x.SapSystems, colmap =>
{
colmap.Table("sapgui");
colmap.Key(x => x.Column("Installation"));
colmap.Inverse(true);
colmap.Lazy(CollectionLazy.NoLazy);
colmap.Cascade(Cascade.None);
colmap.Fetch(CollectionFetchMode.Join);
//colmap.Where("Type = 1");
}, map => map.OneToMany(m => m.Class(typeof(SAPSystem))));
ManyToOne(x => x.SapSolution, map =>
{
map.Column("Solution");
map.NotNullable(true);
map.Cascade(Cascade.None);
map.Class(typeof(SAPSolution));
});
}
public SAPSystemMap()
{
Id(t => t.ID, t => t.Generator(Generators.Identity));
Property(e => e.Type);
Property(e => e.ExplanationText);
ManyToOne(x => x.SapInstallation, map =>
{
map.Column("Installation");
map.NotNullable(true);
map.Cascade(Cascade.None);
map.Class(typeof(SAPInstallation));
});
}
And the Query:
public IList<SAPSolution> GetProductionSystems()
{
SAPSystem syst = null;
SAPInstallation installation = null;
var subquery = QueryOver.Of(() => syst)
.JoinQueryOver(x => x.SapInstallation, () => installation)
.Where(() => syst.Type == 1)
.Select(x => installation.SapSolution.YPID);
// main Query
var query = Session.QueryOver<SAPSolution>()
.WithSubquery
.WhereProperty(root => root.YPID)
.In(subquery);
return query.List<SAPSolution>();
}
Thank you!
General solution should be:
// this is a subquery (SELECT ....
System syst = null;
Installation installation = null;
var subquery = QueryOver.Of(() => syst)
.JoinQueryOver(x => x.Installation, () => installation)
.Where(() => syst.Type == 1)
.Select(x => installation.Solution.ID)
;
// main Query
var query = session.QueryOver<Solution>()
.WithSubquery
.WhereProperty(root => root.ID)
.In(subquery)
;
var list = query
.Take(10)
.Skip(10)
.List<Solution>();
What we can see, that Solution, Installation and System
System has property Installation (many-to-one)
Installation has property Solution (many-to-one)
This is expect-able, because it goes side by side with one-to-many (it is the reverse mapping)
So, then we create subquery, which returns just solution ID's which belong to system with searched Type.
Main query is flat (the great benefit) and we can use paging on top of it.
We would be able to do that even if there is only one way (one-to-many). But that will generate more complicated SQL query ... and does not make sense. In C# we can have both relations...
EXTEND:
You did a great job. Your mapping and query is really cool. But there is one big but: LAZY is what we should/MUST use. Check this:
NHibernate is lazy, just live with it, by Ayende
So, our, collections cannot be FETCHING with a JOIN, because that will multiply the result (10 solutions * 100 installation * 10 systems == 10000 results)
Bag(x => x.SapSystems, colmap =>
{
...
// THIS IS not good way
colmap.Lazy(CollectionLazy.NoLazy);
colmap.Fetch(CollectionFetchMode.Join);
We should use LAZY as possible. To avoid later 1 + N issue, we can use batch-fetching (for example check this)
How to Eager Load Associations without duplication in NHibernate?
So, our collections should be mapped like this:
Bag(x => x.SapSystems, colmap =>
{
...
// THIS IS not good way
colmap.Lazy(CollectionLazy.Lazy);
colmap.BatchSize(100);
With this setting, the query will really use only the root object and related collections will be loaded very effectively
I have a linq query that returns the last page a user looked at based on a table of page hits. The fields are simply TimeStamp, UserID and URL which are logged from user activity. The query looks like this:
public static IQueryable GetUserStatus()
{
var ctx = new AppEntities();
var currentPageHits = ctx.Pagehits
.GroupBy(x => x.UserID)
.Select(x => x.Where(y => y.TimeStamp == x.Max(z => z.TimeStamp)))
.SelectMany(x => x);
return currentPageHits.OrderByDescending(o => o.TimeStamp);
}
The query works perfectly but runs slowly. Our DBA assures us that the table has indexes in all the right places and that the trouble must be with the query.
Is there anything inherently wrong or BAD with this, or is there a more efficient way of getting the same results?
You could try:
var currentPageHits2 = ctx.Pagehits
.GroupBy(x => x.UserID)
.Select(x => x.OrderByDescending(y => y.TimeStamp).First())
.OrderByDescending(x => x.TimeStamp);
But the speed should be the same.
Note that there is a subtle difference between this query and yours... With yours, if a UserId has two "max TimeStamp" PageHits with the same TimeStamp, two "rows" will be returned, with this one only one will be returned.
So you try to implement DENSE_RANK() OVER (PARTITION BY UserID ORDER BY TimeStamp DESC) with LINQ? So all latest records per user-group according to the Timestamp. You could try:
public static IQueryable GetUserStatus()
{
var ctx = new AppEntities();
var currentPageHits = ctx.Pagehits
.GroupBy(x => x.UserID)
.SelectMany(x => x.GroupBy(y => y.TimeStamp).OrderByDescending(g=> g.Key).FirstOrDefault())
.OrderByDescending(x => x.TimeStamp);
return currentPageHits;
}
So it's grouping the user-group by TimeStamp, then it takes the latest group(one or more records in case of ties). The SelectMany flattens the goups to records. I think this is more efficient than your query.
I am using NHibernate and while traversing my code I came upon two functions that are called in sequence. They are probably a school example of 1) extra database round trip and 2) in-memory processing at the application side. The code involved is:
// 1) Getting the surveys in advance
var surveys = DatabaseServices.Session.QueryOver<Survey>()
.Where(x => x.AboutCompany.IsIn(companyAccounts.ToList()))
// Actual query that can be optimized
var unverifiedSurveys = DatabaseServices.Session.QueryOver<QuestionInSurvey>()
.Where(x => x.Survey.IsIn(surveys.ToList()))
.And(x => x.ApprovalStatus == status)
.List();
// 2) In-memory processing
return unverifiedSurveys.Select(x => x.Survey).Distinct()
.OrderByDescending(m => m.CreatedOn).ToList();
I have read that the actual Distinct() operation with the QueryOver API can be done using 1 .TransformUsing(Transformers.DistinctRootEntity)
Could anyone give an example how the queries can be combined thus having one round trip to the database and no application-side processing?
The most suitable way in this scenario is to use Subselect. We will firstly create the detached query (which will be executed as a part of main query)
Survey survey = null;
QueryOver<Survey> surveys = QueryOver.Of<Survey>(() => survey)
.Where(() => survey.AboutCompany.IsIn(companyAccounts.ToList()))
.Select(Projections.Distinct(Projections.Property(() => survey.ID)));
So, what we have now is a statement, which will return the inner select. Now the main query:
QuestionInSurvey question = null;
var query = session.QueryOver<QuestionInSurvey>(() => question)
.WithSubquery
.WhereProperty(() => qeustion.Survey.ID)
.In(subQuery) // here we will fitler the results
.And(() => question.ApprovalStatus == status)
.List();
And what we get is the:
SELECT ...
FROM QuestionInSurvey
WHERE SurveyId IN (SELECT SurveyID FROM Survey ...)
So, in one trip to DB we will recieve all the data, which will be completely filtered on DB side... so we are provided with "distinct" set of values, which could be even paged (Take(), Skip())
This might be something like this, which requires a distinct projection of all properties of Survey. I guess there is a better solution, but can not get to it ;-) Hope this will help anyway.
Survey surveyAlias = null;
var result =
session.QueryOver<QuestionInSurvey>()
.JoinAlias(x => x.Survey, () => surveyAlias)
.WhereRestrictionOn(() => surveyAlias.AboutCompany).IsIn(companyAccounts.ToList())
.And(x => x.ApprovalStatus == status)
.Select(
Projections.Distinct(
Projections.ProjectionList()
.Add(Projections.Property(() => surveyAlias.Id))
.Add(Projections.Property(() => surveyAlias.AboutCompany))
.Add(Projections.Property(() => surveyAlias.CreatedOn))
)
)
.OrderBy(Projections.Property(() => surveyAlias.CreatedOn)).Desc
.TransformUsing(Transformers.AliasToBean<Survey>())
.List<Survey>();