I have a table where it has the columns like IsAgreed, IsOther, IsEquipped. On the UI I am showing 3 check boxes where one can select single or multiple check boxes. The data is getting saved to db as expected. Now I am trying to select the data in entity framework as follows
from tbl context.TableNames select new {
Conitions= tbl.IsOther ? tbl.OtherText : tbl.IsAgreed ? "Agreed :
tbl.IsEquipped? "Equipped" : "" }
Which is giving only one selection when the multiple selection are made. I would like to concat and result the data so that it can be
OtherText, Agreed, Equipped
OtherText, Equipped
Agreed, Equipped
Is it possible to concatenate and give the expected output
You can create an array of strings based on conditions, after it can be formatted as desired. Please pay attention to the comment i wrote in the code sample.
var conditions = context.TableNames.Select(tbl => new
{
tbl.IsOther,
tbl.IsAgreed,
tbl.IsEquipped
})
.AsEnumerable() //Should be used with caution. Because it will load each record to memory. It also switches "LINQ to Entities" to "LINQ to Objects", so we can use string.Join.
.Select(c => new
{
Conditions = string.Join(", ", new string[] { c.IsOther ? "OtherText" : "", c.IsAgreed ? "Agreed" : "", c.IsEquipped ? "Equipped" : "" }.Where(s => !string.IsNullOrEmpty(s)))
});
Related
I am new in Entity Framework and I have a little question.
Is it possible to compare in "Where" with a number.
I will add code example.
var source = db.Book.Where(book => book.Count > 0);
So, I need to get all book items where count more than zero.
Thanks in advance for your help!
Here is the structure of database
I'm not sure why you are trying to query the entire table to check if there is any record, yet you can do something like:
var query = context.Books.Any() ? context.Books.ToList() : null;
if (query is not null)
{
query.ForEach(b =>
{
Console.WriteLine($"ID:{b.Id}, Title:{b.Title}");
});
}
However, if you are trying to find out if there is duplication available, you can use the following query:
var query = context.Books.FirstOrDefault(b => b.Title == "some title")
is not null ? context.Books.ToList() : null;
if (query is not null)
{
query.ForEach(b =>
{
Console.WriteLine($"ID:{b.Id}, Title:{b.Title}");
});
}
By the way, I don't think it is a good idea to have such a scenario.
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 table called "UserAnswers".below screenshot contains table data
I want to get data by surveyId and group by CreatedBy column.
for an example
There is a user called "amara#gmail.com".this user contains 4 records for a SurveyId.
I want to get this like below
Answers : [
{"2"},
{"1","0","1","1"},
{"1","2","4","3"},
{"Blue"}]
But my code returns this array for every rows.I meant duplicate records returning.
Here is my code
var qstns = await (from uans in _context.UserAnswers
where uans.SurveyId == id
select new UserAnswersReturnDto
{
UserEmail = uans.CreatedBy,
Qustns = (from ans in _context.UserAnswers
where ans.CreatedBy == uans.CreatedBy
select new UserAnswersSet
{
QNo = ans.QNo,
Ansrs = JsonConvert.DeserializeObject<JArray>(string.IsNullOrEmpty(ans.Answers) ? "[]" : ans.Answers)
}).ToArray()
}).ToListAsync();
So how to solve this issue.I opened many questions for this problem,but no one answered.Please help me.Thanks in advanced
You need to actually group your data before returning:
I used LINQ Lambda notation, but it should be quite easy to translate back to query if you're so inclined:
var qstns = _context.UserAnswers.Where(uans => uans.SurveyId == id)
.GroupBy(uans => uans.CreatedBy)
.Select(grans => new UserAnswersReturnDto {
UserEmail = grans.Key,
Qustions = grans.Select(ans => new UserAnswersSet() {
QNo = ans.QNo,
Ansrs = ans.Answers
}).ToList()
} ).ToList();
I didn't have time to double-check this, but I hope it serves as a guide to help you solve your issue!
There is no group by statement in your linq query.
I'm trying to write a query to get all restaurant tables if exists or not a opened sale on it.
if a sale exists on a table I want to get the sum and couple details.that is my code:
db.SALETABLES
.GroupJoin(
db.SALES.Where(c => c.CLOSEDTIME == null),
t => t.ID,
sa => sa.ID_TABLE,
(ta, s) => new
{
ta.ID,
ta.DESCRIPTION,
NR_SALE = s.Any() ? s.First().NR_SALE : 0,
IDSALE = s.Any() ? s.First().ID : 0,
IDUSER = s.Any() ? s.First().IDUSER : 0,
USERNAME = s.Any() ? s.First().USERS.USERNAME :"" ,
SALESUM = s.Any() ? s.First().SALES_DETAIL.Sum(p => p.PRICE * p.CANT) : 0
}
but got this error:
Exception thrown: 'System.InvalidOperationException' in
System.Private.CoreLib.dll
thanks for any help
You don't specify the exception, but I assume it's about client-side evaluation (CSE), and you configured EF to throw an exception when it occurs.
It may be First() that triggers CSE, or GroupJoin. The former can easily be fixed by using FirstOrDefault(). The GroupJoin has more to it.
In many cases it isn't necessary to use GroupJoin at all, of Join, for that matter. Usually, manually coded joins can and should be replaced by navigation properties. That doesn't only make the code better readable, but also avoids a couple of issues EF 2.x has with GroupJoin.
Your SaleTable class (I'm not gonna follow your database-driven names) should have a property Sales:
public ICollection<Sale> Sales { get; set; }
And if you like, Sale could have the inverse navigation property:
public SaleTable SaleTable { get; set; }
Configured as
modelBuilder.Entity<SaleTable>()
.HasMany(e => e.Sales)
.WithOne(e => e.SaleTable)
.HasForeignKey(e => e.SaleTableId) // map this to ID_TABLE
.IsRequired();
Now using a table's Sales property will have the same effect as GroupJoin —a unique key, here a SaleTable, with an owned collection— but without the issues.
The next improvement is to simplify the query. In two ways. 1. You repeatedly access the first Sale, so use the let statement. 2. The query is translated into SQL, so don't worry about null references, but do prepare for null values. The improved query will clarify what I mean.
var query = from st in db.SaleTables
let firstSale = st.Sales.FirstOrDefault()
select new
{
st.ID,
NrSale = (int?)firstSale.NrSale ?? 0,
IdSale = (int?)firstSale.ID ?? 0,
...
SalesSum = (int?)firstSale.SalesDetails.Sum(p => p.Price * p.Cant) ?? 0
}
Using NrSale = firstSale.NrSale, would throw an exception for SaleTables without Sales (Nullable object must have a value).
Since the exception is by the EF Core infrastructure, apparently you are hitting current EF Core implementation bug.
But you can help EF Core query translator (thus avoiding their bugs caused by missing use cases) by following some rules when writing your LINQ to Entities queries. These rules will also eliminate in most of the cases the client evaluation of the query (or exception in EF Core 3.0+).
One of the rules which is the origin of issues with this specific query is - never use First. The LINQ to Objects behavior of First is to throw exception if the set is empty. This is not natural for SQL which naturally supports and returns NULL even for values which normally do not allow NULL. In order to emulate the LINQ to Objects behavior, EF Core has to evaluate First() client side, which is not good even if it works. Instead, use FirstOrDefault() which has the same semantics as SQL, hence is translated.
To recap, use FirstOrDefault() when you need the result to be a single "object" or null, or Take(1) when you want the result to be a set with 0 or one elements.
In this particular case, it's better to incorporate the 0 or 1 related SALE rule directly into the join subquery, by removing the GroupJoin and replacing it with SelectMany with correlated Where. And the Any() checks are replaced with != null checks.
With that said, the modified working and fully server translated query looks like this:
var query = db.SALETABLES
.SelectMany(ta => db.SALES
.Where(s => ta.ID == s.ID_TABLE && s.CLOSEDTIME == null).Take(1), // <--
(ta, s) => new
{
ta.ID,
ta.DESCRIPTION,
NR_SALE = s != null ? s.NR_SALE : 0,
IDSALE = s != null ? s.ID : 0,
IDUSER = s != null ? s.IDUSER : 0,
USERNAME = s != null ? s.USERS.USERNAME : "",
SALESUM = s != null ? s.SALES_DETAIL.Sum(p => p.PRICE * p.CANT) : 0
});
I have two model classes first one is "Ticket" and other is "ExpTicket" there is only one additional column/properties in ExpTicket and others properties are same in both lists. I extract the data from database in the form of ExpTicket list and then re-assign all column/properties to Ticket List except one additional column which does not exist in Ticket list.
But iam unable to assign data from "ExpTicket" list to "Ticket" list. If anyone can timely help I shall be very thankful. Following is the code which i need to convert From ExpTicket into "Ticket" List but failed. Please help.
var GetTicket = ticketRepository.ExpTicket(r => r.TicketId == TicketId).ToList();
List<Ticket> CTicket = GetTicket.ToList();
First you have:
var GetTicket = ticketRepository.ExpTicket(r => r.TicketId == TicketId).ToList();
Then make a query:
var CTickets = (from t in GetTicket
select new Ticket{field1=t.field1,field2=t.field2...}).ToList();
Or just readjust your model to use TPT (Table per type, Table per type code first) Good luck
var CTickets = new List<Ticket>();
var ExpTicket = ticketRepository.Where(r => r.TicketId == TicketId);
foreach (var ticket in ExpTicket)
{
CTickets.Add(new Ticket { TicketId = ticket.TicketId, ... and so on });
}
// CTickets is the new list of tickets