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 :(
Related
I have entities like Product(Id, Name) and Keyword(Id, Description), and there is a many-to-many relationship between them.
The essence of my task is the following, I need to do a full-text search on Name and Description columns, using EF CORE 6
I already have some SQL code that works fine.
SELECT a."Id", a."Name" as name, k.txt
FROM "Products" AS a
LEFT JOIN (
SELECT x."ProductsId" as Id, string_agg(y."Description", ' ') as txt
FROM "ProductKeywords" x
JOIN "Keywords" y ON y."Id" = x."KeywordId"
GROUP BY 1
) k ON a."Id" = k.Id
WHERE to_tsvector(concat_ws(' ', a."Name", k.txt))
## to_tsquery('Some text');
And I need to write some LINQ code that will do something similar, but I have a problem with string_agg, and I don't understand how to implement it in LINQ and EF CORE will reflect it correctly
I tried to do the following
var products = _context.Products
.Select(e => new
{
Id = e.Id,
Name = e.Name,
Keywords = string.Join(" ", e.Keywords.Select(q => q.Description))
}).Where(e => EF.Functions.ToTsVector(e.Keywords).Matches("Some text")).ToList();
But I get an error, and it's most likely because of string.Join
could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'
Got the result, using linq2db
var query = _context.Products.ToLinqToDB()
.LeftJoin(_context.ProductsKeywords.ToLinqToDB().GroupBy(r => r.ProductId).Select(e => new {
Key = e.Key,
Txt = e.StringAggregate(",", t => t.Keyword.Description).ToValue()
}),
(product, productKeyword) => product.Id == productKeyword.Key,
(i, j) => new {
Id = i.Id,
Txt = j.Txt
}).Select(e => new {
Id = e.Id,
Txt = EF.Functions.ToTsVector(e.Txt)
}).Where(w => w.Txt.Matches("Some text"));
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 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.
I have an entity set called Entities which has a field Name and a field Version. I wish to return the object having the highest version for the selected Name.
SQL wise I'd go
Select *
from table
where name = 'name' and version = (select max(version)
from table
where name = 'name')
Or something similar. Not sure how to achieve that with EF. I'm trying to use CreateQuery<> with a textual representation of the query if that helps.
Thanks
EDIT:
Here's a working version using two queries. Not what I want, seems very inefficient.
var container = new TheModelContainer();
var query = container.CreateQuery<SimpleEntity>(
"SELECT VALUE i FROM SimpleEntities AS i WHERE i.Name = 'Test' ORDER BY i.Version desc");
var entity = query.Execute(MergeOption.OverwriteChanges).FirstOrDefault();
query =
container.CreateQuery<SimpleEntity>(
"SELECT VALUE i FROM SimpleEntities AS i WHERE i.Name = 'Test' AND i.Version =" + entity.Version);
var entity2 = query.Execute(MergeOption.OverwriteChanges);
Console.WriteLine(entity2.GetType().ToString());
Can you try something like this?
using(var container = new TheModelContainer())
{
string maxEntityName = container.Entities.Max(e => e.Name);
Entity maxEntity = container.Entities
.Where(e => e.Name == maxEntityName)
.FirstOrDefault();
}
That would select the maximum value for Name from the Entities set first, and then grab the entity from the entity set that matches that name.
I think from a simplicity point of view, this should be same result but faster as does not require two round trips through EF to sql server, you always want to execute query as few times as possible for latency, as the Id field is primary key and indexed, should be performant
using(var db = new DataContext())
{
var maxEntity = db.Entities.OrderByDecending(x=>x.Id).FirstOrDefault()
}
Should be equivalent of sql query
SELECT TOP 1 * FROM Entities Order By id desc
so to include search term
string predicate = "name";
using(var db = new DataContext())
{
var maxEntity = db.Entities
.Where(x=>x.Name == predicate)
.OrderByDecending(x=>x.Id)
.FirstOrDefault()
}
I think something like this..?
var maxVersion = (from t in table
where t.name == "name"
orderby t.version descending
select t.version).FirstOrDefault();
var star = from t in table
where t.name == "name" &&
t.version == maxVersion
select t;
Or, as one statement:
var star = from t in table
let maxVersion = (
from v in table
where v.name == "name"
orderby v.version descending
select v.version).FirstOrDefault()
where t.name == "name" && t.version == maxVersion
select t;
this is the easiest way to get max
using (MyDBEntities db = new MyDBEntities())
{
var maxReservationID = _db .LD_Customer.Select(r => r.CustomerID).Max();
}
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();