I am using MySQL DB with ef core all works fine but the following query does nto return expected result.
var query = _context.ServiceData.
Include(x => x.Country)
.Include(x=>x.Country.CountryLocale)
.Where(x=>x.Country.CountryLocale.Any(l=>l.Locale == "en-US"));
After executing and doing
query.First().Country.CountryLocale.Count // Returns count of greater than 1 when expected count is 1
The table only has 2 entries and the above pulls both when only 1 is expected.
Table Layout
Id Name Locale
1 Test en-US
2 Test en-GB
All examples I have seen seem to suggest doing it how I am doing it so not sure what I am missing.
Here is the sql generated by above Linq
SELECT `a`.`Id`, `a`.`ServiceDataCode`, `a`.`CountryId`, `a`.`Enabled`, `a`.`LastUpdated`, `a`.`TimezoneId`, `c`.`Id`, `c`.`DialingCode`, `c`.`Enabled`, `c`.`IsoNumeric`, `c`.`IsoThreeLetterCode`, `c`.`IsoTwoLetterCode`, `c`.`LastUpdated`, `c0`.`Id`, `c0`.`IsoTwoLetterCode`, `c0`.`LastUpdated`, `c0`.`Locale`, `c0`.`Name`
FROM `ServiceData` AS `a`
INNER JOIN `CountryData` AS `c` ON `a`.`CountryId` = `c`.`Id`
LEFT JOIN `CountryLocale` AS `c0` ON `c`.`IsoTwoLetterCode` = `c0`.`IsoTwoLetterCode`
WHERE EXISTS (
SELECT 1
FROM `CountryLocale` AS `c1`
WHERE (`c`.`IsoTwoLetterCode` = `c1`.`IsoTwoLetterCode`) AND (`c1`.`Locale` = 'en-US'))
ORDER BY `a`.`Id`, `c`.`Id`, `c0`.`Id`
I guess a stored procedure is another option but wanted to do it without.
Well, here is an object query with a right paths of country and specific country locale that belong to first service data:
using (var query = _context.ServiceData
.Include("Country.CountryLocale")
.Where(x => x.ServiceData.CountryId == x.Country.Id)
.Where(x => x.Country.IsoTwoLetterCode == x.Country.CountryLocale.IsoTwoLetterCode)
.Where(x => x.Country.CountryLocale.Locale == "en-US"))
{
query.FirstOrDefault();
}
Hope this helps.
Related
Select *,
(Select DefaultStartDay from Scheduler.ProgramSettings ps where ps.DefaultStartDay = s.Id ) [DefaultStartDay]
from Scheduler.Schedules s
where ScheduleType = 2;
I want to write above SQL query in EF Core, Specially I need subquery in select list to get data from another table with specific condition.
please refer image.Sample Data with SQL Query
I have tried below EF Core but getting wrong result.
var model = _context.Schedules
.Where(s => s.ScheduleType == 2)
.Select(rv => new ProgramSetting
{
Id = rv.Id,
ProgramTemplateId = rv.ProgramTemplateId,
IsActive = rv.IsActive,
DefaultStartDay = rv.Id
}).ToArray();
The SQL query is wrong and this is a misuse of EF Core.
First, that SQL will fail if there's more than 1 result from the subquery. Even in SQL you'd need a different query. An INNER JOIN would return the same results without failing if there are multiple matches.
Select s.*,ps.DefaultStartDay
from Scheduler.Schedules s
inner join Scheduler.ProgramSettings ps on ps.DefaultStartDay = s.Id
where ScheduleType = 2;
Second, using LINQ to emulate SQL is a misuse of both EF Core and LINQ. EF isn't a replacement for SQL, it's an ORM. Its job is to give the impression of working with in-memory objects instead of tables, not allow you to write SQL queries in C#
It's the ORM's job to generate JOINs as needed from the relations between entities (not tables). In this case, if Schedule has a ProgramSettins property, EF would generate the necessary joins automatically. Loading an entire schedule object could be as simple as :
var schedules=_context.Schedules
.Incule(sch=>sch.ProgramSettings)
.Where(s => s.ScheduleType == 2)
.ToArray();
Include is used to eagerly load the settings, not to force a JOIN.
If a Select clause is used that requires a property from ProgramSettings, the JOIN will be generated automatically, eg :
var namesAndDays=_context.Schedules
.Where(s => s.ScheduleType == 2)
.Select(s=>new {
Name = s.Name,
StartDay = s.ProgramSettings.DefaultStartDay
})
.ToArray();
I have an existing linq query which gets some data into a view model object. This is working fine.
I want to add a new property for data from child table which will have column values from a child table in a comma separated string format.
Problem: I am not able to concatenate the results using string.join
Simplified version of tables showing only relevant fields
part
id
part number
1
ABC1
2
DEF1
vendor
id
vendorname
1
acme
2
john
vendor part name (vendor specific part number)
partid
vendorid
partname
1
1
GDSE-553-32
1
2
JWWVV-HH-01
simplified version of query
result = (from p in DBContext.Parts.Where(w => w.EquipmentId == eId)
select new PartModel
{
Id = p.Id,
Number = p.PartNumber,
VendorPartNames= String.Join(",", DBContext.VendorPartName.Where(w => w.PartId == p.Id).Select(s => s.PartName))//this line causes exception (shown below)
});
Exception:
LINQ to Entities does not recognize the method 'System.String Join(System.String, System.String[])' method, and this method cannot be translated into a store expression.
Please note: the actual query has some joins and other columns, so please dont suggest solutions that requires joins.
If I change the "VendorPartName" to a List type , I can get the results without any problems.
My only problem is in "How to convert the results for "VendorPartName" property to a comma separated strings?"
eg: based on sample table data provided, it should be
GDSE-553-32, JWWVV-HH-01
Entity Framework does not support String.Join() method.
So, what we can do is to fetch VendorPartNames as a string collection and then we can later separate it with ,.
Note: For this, we would first use an anonymous object and later convert it to PartModel.
So your query would look like this:
var parts = DBContext.Parts
.Where(w => w.EquipmentId == eId)
.Select(p => new {
Id = p.Id,
Number = p.PartNumber,
VendorPartNames = p.VendorPartName.Select(n => n.PartName)
}).ToList();
var result = parts.Select(i => new PartModel {
Id = i.Id,
Number = i.Number,
VendorPartNames = String.Join(",", i.VendorPartNames)
}).ToList();
I have a few tables in my database which are mapped to an edmx. Using the entity framework to return data from these tables, I've encountered a problem where the value in the "name" column from one of my higher level data models is being populated into each model below it.
I'm pulling the data like this:
var query = (from a in context.things
where a.id == 1
select a);
var model = query.Select(a => new modelA()
{
Name = a.name,
Bs = a.Bs.Select(b => new modelB()
{
Name = b.name,
Cs = b.Cs.Select(c => new modelC()
{
Name = c.name,
Ds = c.Ds.Select(d => new modelD()
{
Name = d.name
})
})
})
}).FirstOrDefault();
b.name, c.name and d.name are all returning the same value as a.name despite my database definitely having different values in across these tables.
Could this be a caching issue?
Update
After upgrading the mySql connector to the latest version (6.7.4.0) I am still encountering the error.
After the upgrade it seems i can get 3 levels deep before the data in the name column starts reappearing :(
I'm trying to write a query for a database that will left join a table to a look up table and the results will be returned based on a case statement.
In normal SQL the query would look like this:
SELECT chis_id, chis_detail, cilt.mhcatID, cilt.mhtID, 'TheFileName' =
CASE
WHEN cilt.mhcatID IS NOT NULL AND cilt.mhtID IS NOT NULL THEN chis_linked_filename
END
FROM chis
LEFT JOIN cilt on cilt.mhcatID = chis.mhcat_id AND cilt.mhtID = chis.mht_id
WHERE cch_id = 50
chis is the table being queried, cilt is a look-up table and does not contain any foreign key relationships to chis as a result (chis has existing FK's to mht and mhcat tables by the mhtID and mhcatID respectively).
The query will be used to return a list of history updates for a record. If the join to the cilt lookup table is successful this means that the caller of the query will have permission to view the filename of any associated files for the history updates.
Whilst during my research I've found various posts on here relating on how to do case statements and left joins in Linq to Entity queries, I've not been able to work out how to join on two different fields. Is this possible?
You need to join on an anonymous type with matching field names like so:
var query = from x in context.Table1
join y in context.Table2
on new { x.Field1, x.Field2 } equals new { y.Field1, y.Field2 }
select {...};
A full working example using the an extra from instead of a join would look something like this:
var query = from chis in context.Chis
from clit in context.Clit
.Where(x => x.mhcatID = chis.mhcat_id)
.Where(x => x.mhtID = chis.mht_id)
.DefaultIfEmpty()
select new
{
chis.id,
chis.detail,
cilt.mhcatID,
cilt.mhtID,
TheFileName = (cilt.mhcatID != null && cilt.mhtID != null) ? chis.linked_filename : null
};
Based on what Aducci suggested, I used a group join and DefaultIsEmpty() to get the results I wanted. For some reason, I couldn't get DefaultIfEmpty() didn't work correctly on its own and the resulting SQL employed an inner join instead of a left.
Here's the final code I used to get the left join working:
var query = (from chis in context.chis
join cilt in context.cilts on new { MHT = chis.mht_id, MHTCAT = chis.mhcat_id } equals new { MHT = cilt.mhtID, MHTCAT = cilt.mhcatID } into tempCilts
from tempCilt in tempCilts.DefaultIfEmpty()
where chis.cch_id == 50
select new {
chisID = chis.chis_id,
detail = chis.chis_detail,
filename = chis.chis_linked_filename,
TheFileName = (tempCilt.mhcatID != null && tempCilt.mhtID != null ? chis.chis_linked_filename : null),
mhtID = chis.mht_id,
mhtcatID = chis.mhcat_id
}).ToList();
I am working on a new project and we are using Entity Framework and the dev lead would like to use lambda queries whenever possible. One thing we are having a hard time figuring out is how to select two columns specifically. Also how to select distinct. We have a table that has multiple entries for a vendor but we want to just get a list of vendors and load to a dictionary object. It fails because as written it is trying to add a key value that has already been added. Take the following query.
Dictionary<int, string> dict = new Dictionary<int, string>();
dict = GetWamVendorInfo().AsEnumerable()
.Where(x => x.vendor_name != null && x.vendor_id != null)
//.Select(x => x.vendor_id).Distinct()
.Take(2)
.ToDictionary(o => int.Parse(o.vendor_id.ToString()), o => o.vendor_name);
What I would like to do is select just vendor_id and vendor_name so we can get just the distinct records.
Any help would be greatly appreciated.
Thanks,
Rhonda
Use an anonymous type:
// earlier bit of query
.Select(x => new { VendorId = x.vendor_id, VendorName = x.vendor_name } )
.Distinct()
.ToDictionary(o => o.VendorId, o => o.VendorName);
I've removed the call to Take(2) as it wasn't clear why you'd want it - and also removed the parsing of VendorId, which I would have expected to already be an integer type.
Note that you should almost certainly remove the AsEnumerable call from your query - currently you'll be fetching all the vendors and filtering with LINQ to Objects. There's also no point creating an empty dictionary and then ignoring it entirely. I suspect your complete query should be:
var vendors = GetWamVendorInfo()
.Select(x => new { VendorId = x.vendor_id,
VendorName = x.vendor_name } )
.Distinct()
.ToDictionary(o => o.VendorId,
o => o.VendorName);
As an aside, you should ask your dev lead why he wants to use lambda expressions (presumably as opposed to query expressions) everywhere. Different situations end up with more readable code using different syntax options - it's worth being flexible on this front.
Just use an anonymous object:
var vendors = GetWamVendorInfo().AsEnumerable()
.Where(x => x.vendor_name != null && x.vendor_id != null)
.Select(new {x.vendor_id, x.vendor_name})
.Take(2)
That's it. You can now work with vendors[0].vendor_id, vendors[0].vendor_name, and so on.