I need to build a dynamic where clause in a Linq statement with multiple joins.
.Net 3.5
Linq-To-Sql
I have these incoming parameters for the Linq statement, only the "UID" is required.
int uid = 23702; // <-- Only one Required
string courseNumber = "";
string title = "";
int? categoryId = null;
int? typeId = null;
I've been testing this out in LinqPad and while I've gotten the query to work with all Where clauses in place, the Nullable int parameters end up returning incorrect results.
Here's my Linq statement:
var ci = course_instances;
var query = courses.Join(ci,
c => c.course_id,
i => i.course_id,
(c, i) => new
{
c = c,
i = i
}).Join(user_courses,
temp => temp.i.instance_id,
uc => uc.instance_id,
(temp, uc) => new
{
temp = temp,
uc = uc
})
.Where (temp1 => (temp1.uc.uid == uid))
.Where (temp1 => (temp1.temp.c.course_number.Contains(courseNumber)))
.Where (temp1 => (temp1.temp.c.title.Contains(title)))
//.Where (temp1 => (temp1.temp.c.course_type_id == typeId))
//.Where (temp1 => (temp1.temp.c.course_category_id == categoryId))
.Select (temp1 => new CourseSearchMyCourses
{
// snipped the many properties
});
I've tried using PredicateBuilder, but it returns the error:
The type arguments for method 'System.Linq.Queryable.Where(System.Linq.IQueryable, System.Linq.Expressions.Expression>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
Here's my PredicateBuilder Linq attempt:
var conditions = PredicateBuilder.True<user_course>();
conditions = conditions.And(c => c.uid == uid);
var ci = course_instances;
var query = courses.Join(ci,
c => c.course_id,
i => i.course_id,
(c, i) => new
{
c = c,
i = i
}).Join(user_courses,
temp => temp.i.instance_id,
uc => uc.instance_id,
(temp, uc) => new
{
temp = temp,
uc = uc
})
.Where (conditions)
.Select (temp1 => new CourseSearchMyCourses
{
// snipped the many properties
});
BTW, I also tried using "System.Linq.Dynamic" using string queries, and got the error the " and " isn't recognized.
Any help is appreciated.
Thanks.
Linq predicates with nullable type variables get translated into a SQL predicate = NULL. But that is totally different than what it should be: IS NULL.
You expect to get the rows where course_type_id is empty, but the = comparison returns no results because NULL is not a value and the comparison returns UNKNOWN. I think that is the cause of your "incorrect results".
If this is your problem, a fix can be found here.
Related
what I want is to include 3 tables in my query and select only the last table fields.
[WebMethod]
public Project[] GetAlll(int passeid)//passed id is the id of fieldteammeber table I am passing
{
var arr = db.Project.Include("FieldTeamMember")
.Include("FieldTeam")
.Where(ft_id=ftm_id and ft_mid=prj_ftm_id and FTM_ID=passeid)
.ToArray();
return arr;
}
want to select the project table fields. there are F keys between tables in the model.
I think this is the query you're looking for based on your description:
int memberId = 1;
var projects = db.Projects
.Where(p => p.FieldTeam
.FieldTeamMembers.Any(ftm => ftm.Id == memberId));
Alternatively, if this is more readable to you:
int fieldTeamMemberId = 1;
var projects = db.FieldTeamMembers.Where(ftm => ftm.Id == memberId)
.Select(ftm => ftm.FieldTeam.Project)
.Distinct();
The EntityModel is defined as:
Personnel has a link to a Country
When executing this code in LinqPad, I see that the SQL which is generated is not optimized (all fields are returned) in the first query ? What am I missing here or doing wrong ?
Query 1 LINQ
var Country = Countries.FirstOrDefault(o => o.Id == 100000581);
var personnelIds = Country.Personnels.Select(p => p.Id).ToArray();
personnelIds.Dump();
Query 1 SQL
exec sp_executesql N'SELECT [t0].[Id], [t0].[Version], [t0].[Identifier], [t0].[Name], , [t0].[UpdatedBy] FROM [Personnel] AS [t0] WHERE [t0].[Country_Id] = #p0',N'#p0 bigint',#p0=100000581
Query 2 LINQ
var Country = Countries.FirstOrDefault(o => o.Id == 100000581);
var personnelIds2 = Personnels.Where(p => p.Country == Country).Select(p => p.Id).ToArray();
personnelIds2.Dump();
Query 2 SQL
exec sp_executesql N'SELECT [t0].[Id] FROM [Personnel] AS [t0] WHERE [t0].[Country_Id] = #p0',N'#p0 bigint',#p0=100000581
The database used is SQL Express 2008. And LinqPad version is 4.43.06
//var Country = Countries.FirstOrDefault(o => o.Id == 100000581);
var personnelIds = context.Personnels
.Where(p => p.Country.Id == 100000581)
.Select(p => p.Id)
.ToArray();
personnelIds.Dump();
Try this, it should be better.
Personnels collection will be populated via lazy loading when accessed, hence retrieving all of the fields from the DB. Here's what's happening...
// retrieves data and builds the single Country entity (if not null result)
var Country = Countries.FirstOrDefault(o => o.Id == 100000581);
// Country.Personnels accessor will lazy load and construct all Personnel entity objects related to this country entity object
// hence loading all of the fields
var personnelIds = Country.Personnels.Select(p => p.Id).ToArray();
You want something more like this:
// build base query projecting desired data
var personnelIdsQuery = dbContext.Countries
.Where( c => c.Id == 100000581 )
.Select( c => new
{
CountryId = c.Id,
PersonnelIds = c.Personnels.Select( p => p.Id )
}
// now do enumeration
// your example shows FirstOrDefault without OrderBy
// either use SingleOrDefault or specify an OrderBy prior to using FirstOrDefaul
var result = personnelIdsQuery.OrderBy( item => item.CountryId ).FirstOrDefault();
OR:
var result = personnelIdsQuery.SingleOrDefault();
Then get the array of IDs if not null
if( null != result )
{
var personnelIds = result.PersonnelIds;
}
Try can also try grouping personnel into a single query
var groups =
(from p in Personnel
group p by p.CountryId into g
select new
{
CountryId = g.Key
PersonnelIds = p.Select(x => x.Id)
});
var personnelIds = groups.FirstOrDefault(g => g.Key == 100000581);
Do you have the ForeignKey explicitly defined in your POCO for Personnel? It's common to leave it out in EF, but adding it would massively simplify both this code and the resulting SQL:
public class Personnel
{
public Country Country { get; set; }
[ForeignKey("Country")]
public int CountryId { get; set; }
. . .
}
> update-database -f -verbose
var ids = db.Personnel.Where(p => p.CountryId == 100000581).Select(p => p.Id).ToArray();
How can I convert this LINQ query from query syntax to method syntax? I am performing a co-related query operation.
var query = (from r in objEntities.Employee
where r.Location == (from q in objEntities.Department
where q.Location == r.Location
select q.Location).FirstOrDefault()
select new
{
FirstName = r.FirstName,
LastName = r.LastName,
Age = r.Age,
Location = r.Location
});
GridView1.DataSource = query;
GridView1.DataBind();
I think you are trying to convert the query to method-based query instead of syntax-based query.
var query = objEntities.Employee
.Where(e => e.Location == objEntities.Department
.Where(d => d.Location == r.Location)
.Select(d => d.Location)
.FirstOrDefault())
.Select(e => new {
FirstName = e.FirstName,
LastName = e.LastName,
Age = e.Age,
Location = e.Location
});
I'm also pretty sure your inner expression within where clause could be replaced with something like that:
.Where(e => objEntities.Department.Any(d => d.Location == e.Location)
Nested queries always have performance issue instead you should use join:
In the lambda expression query should be
var query = objEntities.Employee.Join(objEntities.Department, E => E.Location,
D => D.Location,
(E,D) => new {
FirstName = E.FirstName,
LastName = E.LastName,
Age = E.Age,
Location = E.Location
});
Main Code:
DomainServiceAccountManager d = new DomainServiceAccountManager();
EntityQuery<ListBuy> q = d.GetListMemberBuyQuery();
LoadOperation<ListBuy> l = d.Load(q);
DGListBuy.ItemsSource = l.Entities;
The code:
public IQueryable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new { b.ID, mem.Name, b.Money, b.Tarikh };
return membuy;
}
I get the following message:
Cannot implicitly convert type 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Linq.IQueryable<AccountManager.Web.ListBuy>'. An explicit conversion exists (are you missing a cast?)
You method GetListMemberBuy actually returns an IQueryable of anonymous type instead of an IQueryable of type ListBuy. These are not identical, hence the (compile time?) error.
I can only assume that ListBuy also exists in the database, but if so, then you can remove the anonymous type.
public IQueryable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new ListBuy() { ID = b.ID, Name = mem.Name, Money = b.Money, Tarikh = b.Tarikh }; // <-- new ListBuy() !!
return membuy;
}
If ListBuy does not exist in the database, then you cannot return an IQueryable. Maybe this will work.
public IEnumerable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new { b.ID, mem.Name, b.Money, b.Tarikh };
return membuy
.AsEnumerable()
.Select(b => new ListBuy() {
ID = b.ID, Name = b.Name, Money = b.Money, Tarikh = b.Tarikh
});
}
All this is a bit speculation since you didn't include the ListBuy class definition in your question.
I'm trying to implement a T-SQL equivalent of a where in (select ...) code in LINQ.
This is what I have now:
int contactID = GetContactID();
IEnumerable<string> threadList = (from s in pdc.Messages
where s.ContactID == contactID
group 1 by new { s.ThreadID } into d
select new { ThreadID = d.Key.ThreadID}).ToList<string>();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group new { s } by new { s.ThreadID } into d
let maxMsgID = d.Where(x => x.s.ContactID != contactID).Max(x => x.s.MessageID)
select new {
LastMessage = d.Where(x => x.s.MessageID == maxMsgID).SingleOrDefault().s
};
However, my code won't compile due to this error for the ToList():
cannot convert from
'System.Linq.IQueryable<AnonymousType#1>'
to
'System.Collections.Generic.IEnumerable<string>'
Anyone have any suggestions on how to implement this? Or any suggestions on how to simplify this code?
Your query returns a set of anonymous types; you cannot implicitly convert it to a List<string>.
Instead, you should select the string itself. You don't need any anonymous types.
Change it to
var threadList = pdc.Messages.Where(s => s.ContactID == contactID)
.Select(s => s.ThreadID)
.Distinct()
.ToList();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group s by s.ThreadID into d
let maxMsgID = d.Where(x => x.ContactID != contactID).Max(x => x.MessageID)
select new {
LastMessage = d.Where(x => x.MessageID == maxMsgID).SingleOrDefault()
};