I have a table in database that has some columns.I get a list of some records from this table in my repository class.So I will have something like this:
Now I want to delete records that have the same value in a special column(here in Code column),like this:
I mean I want to have just one of the records that have the same Code column value.
How can I do that in Entity Framework?
Let you are having two table Table1 and table2 and you want to delete all the records
from table1 which are having same code number in table2.
This is your requirement
1.first you have to get all the values of code column of table2
var x = db.table2.Select(p => p.code); Then you have to comapre it with table1
after that you have delete the records for those codes are same.
For that you have to write below piece of code.
foreach (var item in x)
{
var y = db.table1.Where(p => p.code== item).FirstOrDefault();
if (y != null)
{
db.table1.DeleteObject(y);
db.SaveChanges();
}
else
{
}
}
Group by the Code column, skip the first record of each group and delete the rest:
var query = db.Records.GroupBy(r => r.Code)
.Select(grouping => grouping.OrderBy(ent => ent.EntityId).Skip(1));
foreach (var element in query.SelectMany (q => q))
{
db.Records.Remove(element);
}
db.SaveChanges();
Related
enter image description hereI have a code. And there you need to make a grouping by name.
//<date,<partid,amount>>
Dictionary<string, Dictionary<int, double>> emSpending = new Dictionary<string, Dictionary<int, double>>();
foreach (Orders order in db.Orders.ToList())
{
foreach (OrderItems orderitem in order.OrderItems.ToList())
{
if (!emSpending.ContainsKey(order.Date.ToString("yyyy-MM"))) emSpending.Add(order.Date.ToString("yyyy-MM"), new Dictionary<int, double>());
if (!emSpending[order.Date.ToString("yyyy-MM")].ContainsKey(Convert.ToInt32(orderitem.PartID))) emSpending[order.Date.ToString("yyyy-MM")].Add(Convert.ToInt32(orderitem.PartID), 0);
emSpending[order.Date.ToString("yyyy-MM")][Convert.ToInt32(orderitem.PartID)] += Convert.ToDouble(orderitem.Amount);
}
}
DataGridViewColumn col1 = new DataGridViewColumn();
col1.CellTemplate = new DataGridViewTextBoxCell();
col1.Name = "Department";
col1.AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
col1.HeaderText = "Department";
dgvEMSpending.Columns.Add(col1);
foreach (string date in emSpending.Keys)
{
DataGridViewColumn col = new DataGridViewColumn();
col.Name = date;
col.HeaderText = date;
col.AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
col.CellTemplate = new DataGridViewTextBoxCell();
dgvEMSpending.Columns.Add(col);
}
List<string> allKey = emSpending.Keys.ToList();
foreach (string date in allKey)
if (date == "Department") continue;
else
{
dgvEMSpending.Rows.Add();
foreach (int partid in emSpending[date].Keys)
{
dgvEMSpending.Rows[dgvEMSpending.Rows.Count - 1].Cells[0].Value = db.Parts.Where(x => x.ID == partid).SingleOrDefault().Name.GroupBy(Name);
for (int i = 1; i < dgvEMSpending.Columns.Count; i++)
{
if (!emSpending.ContainsKey(dgvEMSpending.Columns[i].Name)) emSpending.Add(dgvEMSpending.Columns[i].Name, new Dictionary<int, double>());
if (!emSpending[dgvEMSpending.Columns[i].Name].ContainsKey(partid)) emSpending[dgvEMSpending.Columns[i].Name].Add(partid, 0);
double val = emSpending[dgvEMSpending.Columns[i].Name][partid];
dgvEMSpending.Rows[dgvEMSpending.RowCount - 1].Cells[i].Value = val;
}
}
}
I tried to use group by myself, but something doesn't work. It just outputs the same names, and I want to group them so that there is a grouping. Pls helped to me.
Ok, a few issues to help you out first. This code:
foreach (Orders order in db.Orders.ToList())
{
foreach (OrderItems orderitem in order.OrderItems.ToList())
{
if (!emSpending.ContainsKey(order.Date.ToString("yyyy-MM"))) emSpending.Add(order.Date.ToString("yyyy-MM"), new Dictionary<int, double>());
if (!emSpending[order.Date.ToString("yyyy-MM")].ContainsKey(Convert.ToInt32(orderitem.PartID))) emSpending[order.Date.ToString("yyyy-MM")].Add(Convert.ToInt32(orderitem.PartID), 0);
emSpending[order.Date.ToString("yyyy-MM")][Convert.ToInt32(orderitem.PartID)] += Convert.ToDouble(orderitem.Amount);
}
}
Right off the bat this is going to trip lazy loading on OrderItems. If you have 10 orders 1-10 you're going to be running 11 queries against the database:
SELECT * FROM Orders;
SELECT * FROM OrderItems WHERE OrderId = 1;
SELECT * FROM OrderItems WHERE OrderId = 2;
// ...
SELECT * FROM OrderItems WHERE OrderId = 10;
Now if you have 100 orders or 1000 orders, you should see the problem. At a minimum ensure that if you are touching a collection or reference on entities you are loading, eager load it with Include:
foreach (Orders order in db.Orders.Include(x => x.OrderItems).ToList())
This will run a single query that fetches the Orders and their OrderItems. However, if you have a LOT of rows this is going to take a while and consume a LOT of memory.
The next tip is "only load what you need". You need 1 field from Order and 2 fields from OrderItem. So why load everything from both tables??
var orderItemDetails = db.Orders
.SelectMany(o => o.OrderItems.Select(oi => new { o.Date, oi.PartId, oi.Amount })
.ToList();
This would give us just the Order date, and each Part ID and Amount. Now that this data is in memory we can group it to populate your desired dictionary structure without having to iterate over it row by row.
var emSpending = orderItemDetails.GroupBy(x => x.Date.ToString("yyyy-MM"))
.ToDictionary(g => g.Key,
g => g.GroupBy(y => y.PartId)
.ToDictionary(g2 => g2.Key, g2 => g2.Sum(z => z.Amount)));
Depending on the Types in your entities you may need to insert casts. This first groups the outer dictionary of the yyyy-MM of the order dates, then it groups the remaining data for each date by part ID, and sums the Amount.
Now relating to your question, from your code example I'm guessing the problem area you are facing is this line:
dgvEMSpending.Rows[dgvEMSpending.Rows.Count - 1].Cells[0].Value = db.Parts
.Where(x => x.ID == partid)
.SingleOrDefault().Name.GroupBy(Name);
Now the question would be to explain what exactly you are expecting from this? You are fetching a single Part by ID. How would you expect this to be "grouped"?
If you want to display the Part name instead of the PartId then I believe you would just want to Select the Part Name:
dgvEMSpending.Rows[dgvEMSpending.Rows.Count - 1].Cells[0].Value = db.Parts
.Where(x => x.ID == partid)
.Select(x => x.Name)
.SingleOrDefault();
We can go one better to fetch the Part names for each used product in one hit using our loaded order details:
var partIds = orderItemDetails
.Select(x=> x.PartId)
.Distinct()
.ToList();
var partDetails = db.Parts
.Where(x => partIds.Contains(x.ID))
.ToDictionary(x => x.ID, x => x.Name);
This fetches us a dictionary set indexed by ID for the part names, it would be done outside of the loop after we had loaded the orderItemDetails. Now we don't have to go to the DB with every row:
dgvEMSpending.Rows[dgvEMSpending.Rows.Count - 1].Cells[0].Value = partDetails[partId];
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"));
How can I select whitch fields should be included for detail table in EF Core.
I tried with this query:
var result= this.context.MainTable
.Include(t => t.DetailTable)
.Select(t => new {
id = t.Id,
values = t.DetailTable.Select(t2 => t2.SomeField)
})
.ToArray();
I would expect this result to single query, but it does not. It automatically execute query one by one for every row in MainTable and select SomeField.
var diaryEntries = (from entry in repository.GetQuery<OnlineDiary.Internal.Model.DiaryEntry>()
.Include("DiaryEntryGradeChangeLog")
.Include("DiaryEntryAction")
join diary in repository.GetQuery<OnlineDiary.Internal.Model.OnlineDiary>()
on entry.DiaryId equals diary.Id
group entry
by diary
into diaryEntriesGroup
select new { Diary = diaryEntriesGroup.Key,
DiaryEntry = diaryEntriesGroup.OrderByDescending(diaryEntry => diaryEntry.DateModified).FirstOrDefault(),
});
This query does not include "DiaryEntryGradeChangeLog" and "DiaryEntryAction" navigation properties, what is wrong in this query?
I have removed join from the query and corrected as per below, and still it populates nothing
var diaryEntries = from entry in repository.GetQuery<OnlineDiary.Internal.Model.DiaryEntry>()
.Include("DiaryEntryGradeChangeLog").Include("DiaryEntryAction")
.Where(e => 1 == 1)
group entry
by entry.OnlineDiary
into diaryEntryGroups
select
new { DiaryEntry = diaryEntryGroups.OrderByDescending(diaryEntry => diaryEntry.DateModified).FirstOrDefault() };
It will not. Include works only if the shape of the query does not change (by design). If you use this query it will work because the shape of the query is still same (OnlineDiary.Internal.Model.DiaryEntry):
var diaryEntries = (from entry in repository.GetQuery<OnlineDiary.Internal.Model.DiaryEntry>()
.Include("DiaryEntryGradeChangeLog")
.Include("DiaryEntryAction");
But once you use manual join, grouping or projection (select new { }) you have changed the shape of the query and all Include calls are skipped.
Edit:
You must use something like this (untested) to get related data:
var diaryEntries = from entry in repository.GetQuery<OnlineDiary.Internal.Model.DiaryEntry>()
group entry by entry.OnlineDiary into diaryEntryGroups
let data = diaryEntryGroups.OrderByDescending(diaryEntry => diaryEntry.DateModified).FirstOrDefault()
select new {
DiaryEntry = data,
GradeChangeLog = data.DiaryEntryGradeChangeLog,
Action = data.DiaryEntryAction
};
or any similar query where you manually populate property for relation in projection to anonymous or unmapped type.
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();