I want to have my EfCore query translated into the following SQL query:
select
c.blablabla
from
codes c
left join lookups l on c.codeId = l.entityid and l.languageCode = <variable - language code of current thread> and l.lookuptype = 'CODE'
where
..something..
order by
l.displayname
Note: tables 'codes' and 'lookups' are not connected! 'lookups' contains a lot of different lookup data in different languages!
I am stuck into limitations of EfCore (like 'NavigationExpandingExpressionVisitor' failed). I don't want to make in-memory filtering, it looks silly to me... Am I missing something obvious?
In perspective, I'd like to make universal method to help sort by displayname (or other lookup name) for different kind of entities - not only codes.
Seems like I figured it out. If there's a better approach - please let me know:
protected override IQueryable<FixCode> SortByDisplayName(IQueryable<FixCode> queryable, string languageCode = null)
{
return queryable
.GroupJoin(
DbContext.FixCodeValues.Where(x =>
x.DomainId == CentralToolConsts.Domains.CENTRAL_TOOLS
&& x.CodeName == CentralToolsFieldTypes.CODE_ORIGIN
&& (x.LanguageCode == languageCode || x.LanguageCode == CentralToolsDbLanguageCodes.English)),
//TODO: this will be a 'selector' parameter
code => code.CodeOriginId,
codeOrigin => codeOrigin.StringValue,
(c, co) => new
{
Code = c,
CodeOrigin = co
}
)
.SelectMany(
x => x.CodeOrigin.DefaultIfEmpty(),
(x, codeOrigin) => new { Code = x.Code, CodeOrigin = codeOrigin }
)
.OrderBy(x => x.CodeOrigin.ShortName)
.Select(x => x.Code);
}
Related
Good evening. Is it possible to combine multiple IQueryable into a single one without using Union in EF Core 2? The main problem is that it doesn't allow to use methods like .Union(), .Except() etc.
It's important that IQueryable should be executed as a single query.
This is what I want to get: toCreateSubquery.Union(toDeleteSubquery)
The queries I want to combine are listed below.
var toCreateSubquery =
validLinks
.Where(
rl => !existingLinks.Any(
el => el.Contract == rl.Contract && el.Estate == rl.Estate)) // Except() doesn't work'
.Select(x => new {x.Contract, x.Estate, Type = ActionType.Create});
var toDeleteSubquery =
existingLinks
.Where(el => !validLinks.Any(rl => el.Contract == rl.Contract && el.Estate == rl.Estate))
.Select(x => new {x.Contract, x.Estate, Type = ActionType.Delete});
This is the visualization of the problem I'm solving.
I want to get the union of these sets without intersection and be able to distinguish belonging to one of these sets.
Just in case, I attach the code of getting these sets:
var validLinks = from ac in _context.AreaContracts
from e in _context.Estate
where (from al in e.AreaLinks select al.Area.Id).Contains(ac.Area.Id) ||
e.Geometry.Intersects(
ac.Area.Geometry)
select new { Contract = ac.Contract.Id, Estate = e.Id };
var existingLinks = from sd in _context.SquareDistributions
select new { Contract = sd.Contract.Id, Estate = sd.Estate.Id };
Thank you for your attention.
I'm trying to select list of Users and for each User JobTitle in correct language depended of strLang selected by user.
Something like that:
IList<User> myData;
myData = Context.Users.Where(u => u.Location == strLocation)
.Include(u => u.JobTitles.Where(e => e.Language == strLang))
.ToList();
But it seems Include doesn't like Where clause
You can't conditionally include only a few entities of a related collection, so you should use projection to get the stuff you need:
IList<User> myData;
var temp = Context.Users.Where(u => u.Location == strLocation)
.Select(u => new
{
User = u;
Locations = u.JobTitles.Where(e => e.Language == strLang));
});
foreach(var t in temp)
{
User user = t.User;
user.Locations = t.Locations;
myData.Add(user);
}
You cannot do it by using the "Include" method since it only take naviation properties.
Disclaimer: I'm the owner of the project EF+ on github.
EF+ Query IncludeFilter allow you to easily filter related entities:
// using Z.EntityFramework.Plus; // Don't forget to include this.
IList<User> myData;
myData = Context.Users.Where(u => u.Location == strLocation)
.IncludeFilter(u => u.JobTitles.Where(e => e.Language == strLang))
.ToList();
You can find the project here
You can find the documentation here
Behind the code, IncludeFilter do exactly like Alexander answer by using a projection.
Spent a lot of time, but still cann't understand how to avoid caching in DbContext.
I attached below entity model of some easy case to demonstrate what I mean.
The problem is that dbcontext caching results. For example, I have next code for querying data from my database:
using (TestContext ctx = new TestContext())
{
var res = (from b in ctx.Buildings.Where(x => x.ID == 1)
select new
{
b,
flats = from f in b.Flats
select new
{
f,
people = from p in f.People
where p.Archived == false
select p
}
}).AsEnumerable().Select(x => x.b).Single();
}
In this case, everything is fine: I got what I want (Only persons with Archived == false).
But if I add another query after it, for example, query for buildings that have people that have Archived flag set to true, I have next things, that I really cann't understand:
my previous result, that is res, will be added by data (there
will be added Persons with Archived == true too)
new result will contain absolutely all Person's, no matter what Archived equals
the code of this query is next:
using (TestContext ctx = new TestContext())
{
var res = (from b in ctx.Buildings.Where(x => x.ID == 1)
select new
{
b,
flats = from f in b.Flats
select new
{
f,
people = from p in f.People
where p.Archived == false
select p
}
}).AsEnumerable().Select(x => x.b).Single();
var newResult = (from b in ctx.Buildings.Where(x => x.ID == 1)
select new
{
b,
flats = from f in b.Flats
select new
{
f,
people = from p in f.People
where p.Archived == true
select p
}
}).AsEnumerable().Select(x => x.b).Single();
}
By the way, I set LazyLoadingEnabled to false in constructor of TestContext.
Does anybody know how to workaround this problem? How can I have in my query what I really write in my linq to entity?
P.S. #Ladislav may be you can help?
You can use the AsNoTracking method on your query.
var res = (from b in ctx.Buildings.Where(x => x.ID == 1)
select new
{
b,
flats = from f in b.Flats
select new
{
f,
people = from p in f.People
where p.Archived == false
select p
}
}).AsNoTracking().AsEnumerabe().Select(x => x.b).Single();
I also want to note that your AsEnumerable is probably doing more harm than good. If you remove it, the Select(x => x.b) will be translated to SQL. As is, you are selecting everything, then throwing away everything but x.b in memory.
have you tried something like:
ctx.Persons.Where(x => x.Flat.Building.Id == 1 && x.Archived == false);
===== EDIT =====
In this case I think you approach is, imho, really hazardous. Indeed you works on the data loaded by EF to interpret your query rather than on data resulting of the interpretation of your query. If one day EF changes is loading policy (for example with a predictive pre-loading) your approach will "send you in then wall".
For your goal, you will have to eager load the data you need to build your "filterd" entity. That is select the building, then foreach Flat select the non archived persons.
Another solution is to use too separate contexts in an "UnitOfWork" like design.
I have a work around for this issue, however I would appreciate it if someone could explain why this is happening and how I would design this for large datasets where my work around would not be viable.
The full error is:
Unable to create a constant value of type 'THPT_Razor.Models.WinType'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
and I am using EF v4.0.
The commented lines are the offending code and the work around is the "For loop"
Thank you in advance.
List<WinType> _atype = db.WinTypes.Where(wt => wt.IsWin == false).ToList();
List<WinType> _wtype = db.WinTypes.Where(wt => wt.IsWin == true).ToList();
string test = _wtype.Where(wt => wt.Value ==0).Select(wt => wt.Description).SingleOrDefault();
List<WinCheckDetails> wcd = db.Wins.Include("UserProfiles").Where(w => w.venueLogId == logid).Select(w => new WinCheckDetails
{
//awarddesc = w.atypeid.HasValue ? _atype.Where( wt=> wt.Value == w.atypeid).Select(wt => wt.Description).SingleOrDefault():string.Empty,
//windesc = _wtype.Where(wt => wt.Value == w.typeid).Select(wt => wt.Description).Single(),
atypeid = w.atypeid,
typeid = w.typeid,
WinId = w.WinId,
other = w.other,
posterid = w.posterid,
confirmed = w.confirmed,
posttime = w.posttime,
game = w.game,
playerid = w.UserProfile.PlayerID,
firstname = w.UserProfile.FirstName,
lastname = w.UserProfile.LastName,
fullname = w.UserProfile.FirstName + " " + w.UserProfile.LastName
}).OrderBy(o => o.game).ToList();
foreach (WinCheckDetails wc in wcd)
{
wc.awarddesc = _atype.Where(wt => wt.Value == wc.atypeid).Select(wt => wt.Description).SingleOrDefault();
wc.windesc = _wtype.Where(wt => wt.Value == wc.typeid).Select(wt => wt.Description).SingleOrDefault();
}
_atype and _wtype are lists of WinType in memory because you are applying ToList() to the queries. With respect to database queries they are collections of constant values because to perform the query in the database they have to be transmitted to the database server as the values they are in memory. EF doesn't support to transfer such constant values or collections of values from memory to the database unless they are values of primitive types (int for example). That's the reason why you get an exception.
Did you try to use _atype and _wtype as IQueryable instead of lists:
IQueryable<WinType> _atype = db.WinTypes.Where(wt => !wt.IsWin);
IQueryable<WinType> _wtype = db.WinTypes.Where(wt => wt.IsWin);
List<WinCheckDetails> wcd = db.Wins
.Where(w => w.venueLogId == logid)
.Select(w => new WinCheckDetails
{
awarddesc = w.atypeid.HasValue
? _atype.Where(wt=> wt.Value == w.atypeid)
.Select(wt => wt.Description).FirstOrDefault()
: string.Empty,
windesc = _wtype.Where(wt => wt.Value == w.typeid)
.Select(wt => wt.Description).FirstOrDefault(),
// ... (unchanged)
}).OrderBy(o => o.game).ToList();
I have removed the Include because it will be ignored anyway when you perform a projection with Select. Also I have replaced SingleOrDefault and Single by FirstOrDefault because both are not supported in a projection (and First neither), only FirstOrDefault is supported.
I am not sure if that will work. But it should remove your exception (but maybe you'll get another one...).
When calling Max() on an IQueryable and there are zero records I get the following exception.
The cast to value type 'Int32' failed because the materialized value is null.
Either the result type's generic parameter or the query must use a nullable type.
var version = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.Max(e => e.Version);
Now I understand why this happens my question is how is the best way to do this if the table can be empty. The code below works and solves this problem, but its very ugly is there no MaxOrDefault() concept?
int? version = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.Select(e => (int?)e.Version)
.Max();
Yes, casting to Nullable of T is the recommended way to deal with the problem in LINQ to Entities queries. Having a MaxOrDefault() method that has the right signature sounds like an interesting idea, but you would simply need an additional version for each method that presents this issue, which wouldn't scale very well.
This is one of many mismatches between how things work in the CLR and how they actually work on a database server. The Max() method’s signature has been defined this way because the result type is expected to be exactly the same as the input type on the CLR. But on a database server the result can be null. For that reason, you need to cast the input (although depending on how you write your query it might be enough to cast the output) to a Nullable of T.
Here is a solution that looks slightly simpler than what you have above:
var version = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.Max(e =>(int?)e.Version);
Try this to create a default for your max.
int version = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.Max(e =>(int?)e.Version) ?? 0;
You could write a simple extension method like this, it returns the default value of type T if no records exist and is then apply Max to that or the query if records exist.
public static T MaxOrEmpty<T>(this IQueryable<T> query)
{
return query.DefaultIfEmpty().Max();
}
and you could use it like this
maxId = context.Competition.Select(x=>x.CompetitionId).MaxOrEmpty();
I couldnt take no for an answer :) I have tested the below and it works, I havent checked the SQL generated yet so be careful, I will update this once I have tested more.
var test = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.MaxOrDefault(x => x.Version);
public static TResult? MaxOrDefault<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
where TResult : struct
{
return source
.Select(selector)
.Cast<TResult?>()
.Max();
}
Try this:
IEnumerable<AlertsResultset> alerts = null;
alerts = (from POA in SDSEntities.Context.SDS_PRODUCT_ORDER_ALERT
join A in SDSEntities.Context.SDS_ALERT on POA.ALERT_ID equals A.ALERT_ID
orderby POA.DATE_ADDED descending
select new AlertsResultset
{
ID = POA.PRODUCT_ORDER_ALERT_ID == null ? 0:POA.PRODUCT_ORDER_ALERT_ID ,
ITEM_ID = POA.ORDER_ID.HasValue ? POA.ORDER_ID.Value : POA.PRODUCT_ID.Value,
Date = POA.DATE_ADDED.Value,
orderType = SDSEntities.Context.SDS_ORDER.Where(o => o.ORDER_ID == POA.ORDER_ID.Value).FirstOrDefault().ORDER_TYPE,
TransactionNumber = POA.PRODUCT_ID.HasValue ? (SDSEntities.Context.SDS_PRODUCT.Where(p => p.PRODUCT_ID == POA.PRODUCT_ID.Value).FirstOrDefault().TRANSACTION_NUMBER) : (SDSEntities.Context.SDS_ORDER.Where(o => o.ORDER_ID == POA.ORDER_ID.Value).FirstOrDefault().TRANSACTION_NUMBER),
Publisher = POA.PRODUCT_ID.HasValue ?
(
SDSEntities.Context.SDS_PRODUCT.Where(p => p.PRODUCT_ID == POA.PRODUCT_ID.Value).FirstOrDefault().PRODUCT_TYPE_NUMBER == "ISSUE" ? (from prod in SDSEntities.Context.SDS_PRODUCT
join ji in SDSEntities.Context.SDS_JOURNAL_ISSUE on prod.PRODUCT_ID equals ji.PRODUCT_ID
join j in SDSEntities.Context.SDS_JOURNAL on ji.JOURNAL_ID equals j.JOURNAL_ID
where prod.PRODUCT_ID == POA.PRODUCT_ID
select new { j.PUBLISHER_NAME }).FirstOrDefault().PUBLISHER_NAME : (from prod in SDSEntities.Context.SDS_PRODUCT
join bi in SDSEntities.Context.SDS_BOOK_INSTANCE on prod.PRODUCT_ID equals bi.PRODUCT_ID
join b in SDSEntities.Context.SDS_BOOK on bi.BOOK_ID equals b.BOOK_ID
where prod.PRODUCT_ID == POA.PRODUCT_ID
select new { b.PUBLISHER_NAME }).FirstOrDefault().PUBLISHER_NAME
)
: (SDSEntities.Context.SDS_ORDER.Where(o => o.ORDER_ID == POA.ORDER_ID.Value).FirstOrDefault().PUBLISHER_NAME),
Alert = A.ALERT_NAME,
AlertType = A.ALERT_TYPE,
IsFlagged = POA.IS_FLAGGED.Value,
Status = POA.ALERT_STATUS
});
how about
var version = ctx.Entries
.Where(e => e.Competition.CompetitionId == storeCompetition.CompetitionId)
.Max(e => (int?)e.Version);
less ugly, more elegant
I want to suggest a merge from the existing answers:
#divega answer works great and the sql output is fine but because of 'don't repeat yourself'
an extension will be a better way like
#Code Uniquely showed. But this solution can output more complex sql as you needed.
But you can use the following extension to bring both together:
public static int MaxOrZero<TSource>(this IQueryable<TSource> source,
Expression<Func<TSource, int>> selector)
{
var converted = Expression.Convert(selector.Body, typeof(int?));
var typed = Expression.Lambda<Func<TSource, int?>>(converted, selector.Parameters);
return source.Max(typed) ?? 0;
}
You can use:
FromSqlRaw("Select ifnull(max(columnname),0) as Value from tableName");