I'm having problem using queries like this with Entity Framework 4 Code First:
var entities = context.TestEntities.Where( e => context.TestEntities2.Count() > 0)
The above query will generate the following exception:
Unable to create a constant value of
type 'TestModel.TestEntities2'. Only
primitive types ('such as Int32,
String, and Guid') are supported in
this context.
The same code works if I use the model designer and generate the POCO-classes and thus using a ObjectContext instead.
EDIT: It works in a console-application but not while using my repository in an MVC 3 project.
EDIT 2: How about this:
var userProfile = ctx.UserProfiles.Where(p => p.User.Id == user.Id).SingleOrDefault();
return ctx.Feeds.Where( f => ctx.ProfileFollowers.Count() > 0 ).ToList();
The above two lines throws the exception. Commenting out the first line solves the problem. Bug in DbContext?
//var userProfile = ctx.UserProfiles.Where(p => p.User.Id == user.Id).SingleOrDefault();
return ctx.Feeds.Where( f => ctx.ProfileFollowers.Count() > 0 ).ToList();
Posted to http://social.msdn.microsoft.com/Forums/en-US/adonetefx/thread/2fb5ceea-9f30-4665-af98-945c6485f60b
Try the Any method:
var q = context.TestEntities.Where(a=>context.TestEntities2.Any());
This code results in the EXISTS clause:
SELECT
[Extent1].[ProductID] AS [ProductID],
...
FROM [dbo].[Products] AS [Extent1]
WHERE EXISTS (SELECT
1 AS [C1]
FROM [dbo].[Regions] AS [Extent2]
UPD: In case of repositories the correct way is to execute the first query and then the second one:
if(context.TestEntities2.Count() > 0)
var q = context.TestEntities.Select(t=>t);
Related
I am not sure why I am getting the error: "Must be reducible node"
This is my query. I am running Core 2 with EF Core 2.2 (So I should have the fixes that occurred in previous versions)
IQueryable<Gizmo> gizmos = _context.Gizmo;
IQueryable<GizmoViewModel> dataReferences = (
gizmos.SelectMany(j => j.DataReferences.Select(r =>
new GizmoViewModel()
{
GizmoId = j.Id,
DataId = r.DataId
}
))
);
Simply (and sadly) you are hitting one of the current EF Core query translation bugs.
Looks like it's caused by the accessing the outer SelectMany lambda parameter inside the inner Select expression.
The workaround is to use another SelectMany overload having a second lambda with both outer and inner parameters (which I guess is used by C# compiler when converting LINQ query syntax):
IQueryable<GizmoViewModel> dataReferences = (
gizmos.SelectMany(j => j.DataReferences, (j, r) =>
new GizmoViewModel()
{
GizmoId = j.Id,
DataId = r.DataId
}
)
);
Try to include DataReferences maybe?
Your code revised:
IQueryable<GizmoViewModel> dataReferences = (
gizmos.SelectMany(j => j.DataReferences.Select(r =>
new GizmoViewModel()
{
GizmoId = j.Id,
DataId = r.DataId
}
))
.Include(m => m.DataReferences)
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 am using dynamic LINQ query in EF4.
Below code throws error: 'New' cannot be resolved into a valid type or function.
var x = ent.OM_COMPANY
.Where(qry)
.OrderBy("it.CM_CODE")
.Select("New(it.CM_CODE, it.CM_NAME)");
What am I doing wrong?
The below code executes without any error.
var x = from cmp in ent.OM_COMPANY
where (qry)
orderby cmp.CM_CODE
select new { cmp.CM_CODE, cmp.CM_NAME };
I don't even know how you got that first code block to compile. Both OrderBy and Select take lambdas not strings. It should be written as:
var x = ent.OM_COMPANY
.Where(qry)
.OrderBy(c => c.CM_CODE)
.Select(c => c.CM_CODE, c.CM_NAME);
Just starting to use LINQ as well as EF.
I have a set of tables in the following configuration:
PublicUtility (UtilityCode) * ----> 1 (UtilityCode) Utility (UtilityCode) 1 -----> * (UtilityCode) UtilityDetail
I have a query in SQL. Based on some other business rules this query will either return 1 value or NULL.
SELECT
#UtilityCode = UtilityDetail.UtilityCode
FROM
UtilityDetail
INNER JOIN PublicUtility ON
PublicUtility.SubdivisionCode = #SubdivisionCode AND
PublicUtility.Year = #PublicUtilityYear AND
PublicUtility.UtilityCode = UtilityDetail.UtilityCode
WHERE
UtilityDetail.DebtPurposeCode = #DebtPurposeCode
How could I rewrite this using LINQ to entities?
using (YourObjectContext ctx = new YourObjectContext())
{
var code = (from ud in ctx.UtilityDetails
join pu in PublicUtility on ud.UtilityCode equals pu.UtilityCode
where ud.DeptPurposeCode == [code_value] && pu.SubdivisionCode == [subdivcode_value] && pu.Year == [year_value]
select new {ud.UtilityCode}).FirstOrDefault();
}
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");