Develop Reference

How to match a list of item to database in C#

I have a list of string
List<string> list = new List<string>();
list.Add("john");
list.Add("David");
list.Add("Sam");
Now I want to check whether my column in database contains these list Items.
var v = db.employee.where(s => s.Content.Contains(list));
My question is how can I match all list items to database column in just one query without using any loop. The query must return result if single list item is matched with column. The query I mentioned above not working. Please help me to solve this.

This will only work with the assumption that your db is an Entity Framework DbContext and that s.Content is a string. If you're using some other ORM then it may not work.
List<string> list = new List<string>();
list.Add("john");
list.Add("David");
list.Add("Sam");
var v = db.employee.Where(s => list.Contains(s.Content)).ToList();

You can do this:
List<string> list = new List<string>();
list.Add("john");
list.Add("David");
list.Add("Sam");
var v = db.employee
.ToList()
// This filtering doesn't happen in your SQL server.
.Where(s => list.Any(x => s.Content.Contains(x)));
You can try to omit .ToList() line but I'm afraid your ORM will not know how to convert the query to SQL.
If you want the whole query to be executed in SQL you should consider building the query this way:
var query = db.employee.AsQueryable();
query = list.Aggregate(query,
(query, name) => query.Where(empl => empl.Content.Contains(name)));

what about:
List<string> list = new List<string> {"john", "Warwick", "Sam"};
var vresult = _db.employee.Where(x => list.Contains(x.Content)).ToList();
please indicate what you are expecting...? like how is it not working?

If return is different than null, exists.
public List<Employee> CheckIfExists(List<string> nameList)
{
if (nameList == null)
{
return null;
}
string inClause = "";
foreach (var item in nameList)
{
inClause = string.Format("{0},{1}", inClause, item);
}
return db.employee.SqlQuery("SELECT * FROM employee WHERE employee.Name IN (#p0)", inClause).ToList();
}

Each element of list will be passed as an argument to s.Content.Contains
and here s is an employee record.
var v = db.employee.Where(s => list.Any(s.Content.Contains));

This might help you,
list with name= {"john", "David", "Sam"}
you want to check if John/David/Sam exists in the employee table.
The below query is to check if the particular name exists in employee or not
var _data = _db.employee.Where(emp => list.Any(li => li.name == emp.name)).ToList();

LINQ in query syntax:
var result = from o in db.employee
where list.Contains(o.Content)
select o;

Contains matches on pairs of items

I have a mapping table in the following form:
Id ReferenceId ReferenceType LinkId
To retrieve a set of combinations, I could run each query separately:
var pairs = new List<Pair>
{
Pair.Create(1000, "Car"),
Pair.Create(2000, "Truck"),
};
var maps = new List<Mapping>();
foreach (var pair in pairs)
{
maps.AddRange(context.Mappings.Where(x => x.ReferenceId = pair.Id && x.ReferenceType == pair.Type).ToList());
}
However, I want to combine these into a single statement to reduce my hits on the db. Is there some form of Contains statement that can work with pairs of objects? Or is it possible to append an OR clause onto an IQueryable within a loop? Any other solutions?

Not sure if it works for your LINQ provider but you could try to join with an anonymous type:
var mapQuery = from p in pairs
join m in context.Mappings
on new { p.Id, p.Type } equals new { m.ReferenceId, m.ReferenceType}
select m;
List<Mapping> maps = mapQuery.ToList();

You could union your queries together.
Something like this:
var pairs = new List<Pair>
{
Pair.Create(1000, "Car"),
Pair.Create(2000, "Truck"),
};
List<Mapping> result =
pairs
.Select(pair =>
context.Mappings.Where(
x => x.ReferenceId == pair.Id
&& x.ReferenceType == pair.Type))
.Aggregate(Queryable.Union)
.ToList();

How to select List in a List by Key through LINQ

I originally have 2 Lists for Keynotes and Tracks. Each of which were then Grouped By date through a Key. See below:
var Keynotes = _keynoteService.GetKeynotesForContentItem(trackPart.ContentItem).GroupBy(k => string.Format("{0}-{1}", k.Timeslot.DayOfYear, k.Timeslot.Year));
var Tracks = GetTracksForContentItem(trackPart.ContentItem);
foreach (var track in Tracks)
{
var trackItem = new TrackItem();
trackItem.Days = new List<TrackDay>();
var trackDays = track.Sessions.GroupBy(s => string.Format("{0}-{1}", s.Timeslot.DayOfYear, s.Timeslot.Year));
foreach(var trackDay in trackDays)
{
var trackKey = trackDay.Key //THIS IS THE KEY I NEED TO MATCH IN Keynotes
var trackKeynotes = Keynotes. //I'm Stuck here
The new lists are now Keynotes and trackDays which are actually lists of lists by Date Keys.
How do I select a list within Keynotes that matches a specific key from trackDays? I already have the key, I just need to know how to select from Keynotes properly to get the right list.
I'm not a LINQ expert so I'd like some help.
I was thinking Keynotes.Select or Keynotes.SingleOrDefault
Any piece of advise would be highly appreciated. Thanks!

var trackKeynotes = Keynotes.SingleOrDefault(g => g.Key == trackKey);

You should do it like this
var result = (from x in Keynotes
join td in TrackDays on x.Key equals td.Key
select x).ToList();

Use Keynotes[trackKey] to index into your grouped items.

Try this instead ::
var trackKeynotes = Keynotes.Where(K => K.Key == trackKey);
Hope this will help !!

Maybe this
var trackKeynotes = Keynotes.Where(x => x.Key == trackKey);
I assume that trackKey is a key of Keynotes.

How do I return data presorted after grabbing them inside a foreach loop?

First, I'm grabbing ClientID. Then, I get all Invoices associated with that ClientID. I want to return data all ordered by InvoiceNumber, descending. Here's my code:
var rvInvoices =
(from i in db.QB_INVOICES_HEADER
where i.ClientID == cId
select i).ToList();
foreach (var itm in rvInvoices)
{
InvoiceModel cm = new InvoiceModel()
{
InvoiceNumber = itm.InvoiceNumber,
InvoiceSentDt = itm.InvoiceSentDt,
InvoiceDt = itm.InvoiceDt,
Amount = itm.Amount,
Term = itm.Term,
ClientName = itm.CI_CLIENTLIST.ClientName
};
listInvoices.Add(cm);
}
return listInvoices;

listInvoices.OrderByDescending(x => x.InvoiceNumber).ToList()

You should try something like this:
var rvInvoices =
(from i in db.QB_INVOICES_HEADER
where i.ClientID == cId
select i).OrderByDescending(x => x.InvoiceNumber);
And I don't see a reason you need to call .ToList().

You can do the order in three places.
In the initial query,
In the foreach, or
In the return
Option 1:
var rvInvoices =
(from i in db.QB_INVOICES_HEADER
where i.ClientID == cId
select i).OrderByDescending(i => i.InvoiceNumber).ToList();
Option 2:
foreach (var itm in rvInvoices.OrderByDescending(i => i.InvoiceNumber))
Option 3:
return listInvoices.OrderByDescending(i => i.InvoiceNumber).ToList();
I would suggest taking route 1 since it will run the order at the database level.

You should order them on the database instead of the client:
var rvInvoices = db.QB_INVOICES_HEADER
.Where(i => i.ClientID == cId)
.OrderByDescending(i => i.InvoiceNumber);

The method you currently have creates multiple lists, has an explicit foreach loop, and needs to have its output sorted. It can be done with just creating a single list, no explicit looping, and with the database doing the sorting for you:
return
(from i in db.QB_INVOICES_HEADER
where i.ClientID == cId
// have the database do the sorting
orderby i.InvoiceNumber descending
select i)
// break out of the DB query to make InvoiceModel
.ToEnumerable()
.Select(itm => new InvoiceModel()
{
InvoiceNumber = itm.InvoiceNumber,
InvoiceSentDt = itm.InvoiceSentDt,
InvoiceDt = itm.InvoiceDt,
Amount = itm.Amount,
Term = itm.Term,
ClientName = itm.CI_CLIENTLIST.ClientName
})
// only create one list as the last step
.ToList();

Entity Framework select distinct name

How can I do this SQL query with Entity Framework?
SELECT DISTINCT NAME FROM TestAddresses

Using lambda expression..
var result = EFContext.TestAddresses.Select(m => m.Name).Distinct();
Another variation using where,
var result = EFContext.TestAddresses
.Where(a => a.age > 10)//if you have any condition
.Select(m => m.name).Distinct();
Another variation using sql like syntax
var result = (from recordset
in EFContext.TestAddresses
.where(a => a.city = 'NY')//if you have any condition
.select new
{
recordset.name
}).Distinct();

Try this:
var results = (from ta in context.TestAddresses
select ta.Name).Distinct();
This will give you an IEnumerable<string> - you can call .ToList() on it to get a List<string>.

The way that #alliswell showed is completely valid, and there's another way! :)
var result = EFContext.TestAddresses
.GroupBy(ta => ta.Name)
.Select(ta => ta.Key);
I hope it'll be useful to someone.

DBContext.TestAddresses.Select(m => m.NAME).Distinct();
if you have multiple column do like this:
DBContext.TestAddresses.Select(m => new {m.NAME, m.ID}).Distinct();
In this example no duplicate CategoryId and no CategoryName i hope this will help you

Entity-Framework Select Distinct Name:
Suppose if you are using Views in which you are using multiple tables and you want to apply distinct in that case first you have to store value in variable & then you can apply Distinct on that variable like this one....
public List<Item_Img_Sal_VIEW> GetItemDescription(int ItemNo)
{
var Result= db.Item_Img_Sal_VIEW.Where(p => p.ItemID == ItemNo).ToList();
return Result.Distinct().ToList();
}
Or you can try this Simple Example
Public Function GetUniqueLocation() As List(Of Integer)
Return db.LoginUsers.Select(Function(p) p.LocID).Distinct().ToList()
End Function

use Select().Distinct()
for example
DBContext db = new DBContext();
var data= db.User_Food_UserIntakeFood .Select( ).Distinct();

In order to avoid ORDER BY items must appear in the select list if SELECT DISTINCT error, the best should be
var results = (
from ta in DBContext.TestAddresses
select ta.Name
)
.Distinct()
.OrderBy( x => 1);

Entity-Framework Select Distinct Name:
Suppose if you are want every first data of particular column of each group ;
var data = objDb.TableName.GroupBy(dt => dt.ColumnName).Select(dt => new { dt.Key }).ToList();
foreach (var item in data)
{
var data2= objDb.TableName.Where(dt=>dt.ColumnName==item.Key).Select(dt=>new {dt.SelectYourColumn}).Distinct().FirstOrDefault();
//Eg.
{
ListBox1.Items.Add(data2.ColumnName);
}
}