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How Create linq query select dynamic custom fileds

I want to reformat the data without going back to the database and in a dynamic way
So that the user can specify what columns he wants to collect
how I can
Write an sql string and execute it like EXECUTE IMMEDIAT in Oracle
Inside C# Linq
want to do a lock like combining two or more fields (multiply - merge...)
ToTable
It only allows me to specify the names of existing fields
FillDataSorce(params P)
{
// p It is a variable containing the field to be queried
//Like
//field1 = d["field1"] ,
//field2 = d["field2"] ,
//field sum = d["field1"] +d["field2"]
BSo.DataSource = from d in dt.AsEnumerable()
select new
{
P.Select(p => p) //col3col2 = d["col1"] + d["col2"] Dynamic field example
};
}

ASP.NET Core Linq query for lists

I have this query that was recently changed to allow searches using lists. However, the logic doesn't seem correct. My initial search logic was as follows:
data = data.where(u=>u.location.contains(FilterInput.RepositoryName)).ToList();
This worked for individual inputs and the logic made sense. In the data result, check if location field contains the Input variable
However in order to handle inputs that are lists, I had to change it to the bottom code which is in this Input list, check if the it contains the location field.
The database outputs data as follows:
Output = {arhde, brhje, ckio}
That means my list input is a small section of what the database contains.
FilterInput.RepositoryName = {a,b,c}
data = (from item in dbContext.Documents
join id in initialData
on item.Id equals id.DocumentId
select new DocumentsListViewModel
{
Id = item.Id,
Name = item.Name,
ApplicationName = item.ApplicationName,
ApplicationSecretKey = item.ApplicationSecretKey,
Link = item.Link,
Location = item.Location,
FileType = item.FileType,
CreatedOn = item.CreatedOn
}).ToList();
if (FilterInput.RepositoryName.Count>0)
{
data = data.Where(u => FilterInput.RepositoryName.Contains(u.Location)).ToList();
}
I don't know if its possible to change this logic to use the first one but accomodate lists as well?

Find within large list using Contains within Linq

I have two large excel files. I am able to get the rows of these excel files into a list using linqtoexcel. The issue is that I need to use a string from one object within the first list to find if it is part of or contained inside another string within an object of the second list. I was trying the following but the process is taking to long as each list is over 70,000 items.
I have tried using an Any statement but have not be able to pull results. If you have any ideas please share.
List<ExcelOne> exOne = new List<ExcelOne>();
List<ExcelTwo> exTwo = new List<ExcelTwo>();
I am able to build the first list and second list and can verify there are objects in the list. Here was my thought of how I would work through the lists to find matching. Note that once I have found the matching I want to create a new class and add it to a new list.
List<NewFormRow> rows = new List<NewFormRow>();
foreach (var item in exOne)
{
//I am going through each item in list one
foreach (var thing in exTwo)
{
//I now want to check if exTwo.importantRow has or
//contains any part of the string from item.id
if (thing.importantRow.Contains(item.id))
{
NewFormRow adding = new NewFormRow()
{
Idfound = item.id,
ImportantRow = thing.importantRow
};
rows.Add(adding);
Console.WriteLine("added one");
}
}
If you know a quicker way around this please share. Thank you.

It's hard to improve this substring approach. The question is if you have to do it here. Can't you do it where you have filled the lists? Then you don't need this additional step.
However, maybe you find this LINQ query more readable:
List<NewFormRow> rows = exOne
.SelectMany(x => exTwo
.Where(x2 => x2.importantRow.Contains(x.id))
.Select(x2 => new NewFormRow
{
Idfound = x.id,
ImportantRow = x2.importantRow
}))
.ToList();

Compare two datatables to find matching values

I have 2 data tables. Each one has one column and I want to compare them and get same values on them but it does not work.
This is my code:
string CurrentRequestUrl = (HttpContext.Current.Request.AppRelativeCurrentExecutionFilePath.ToString());
DataTable dt_Item = ERP.BLL_Menu_Item.Custom_Item_ID(CurrentRequestUrl);
DataTable dt2_SysRole = ERP.BLL_Sys_User_Role.Custom_Role(Convert.ToInt64(App.UserID));
var dtOne = (dt_Item.AsEnumerable()).ToList();
var dtTwo = (dt2_SysRole.AsEnumerable()).ToList();
IEnumerable<DataRow> objIntersectResult = ((dtOne).Intersect((dtTwo))).ToList();
How can I find the matching values?

Intersect does not work here because on DataRow it just compares references. Because all rows are different references you get an empty list. Instead you want to compare values. Therefore you can use Join. But which row do you want to return from both tables? If you want both rows you could create an anonymous type of both:
var objJoinResult = from rowItem in dt_Item.AsEnumerable()
join rowSysRole in dt2_SysRole.AsEnumerable()
on rowItem.Field<string>("ColumnName") equals rowSysRole.Field<string>("ColumnName")
select new { rowItem, rowSysRole };
Output:
foreach (var both in objJoinResult)
{
Console.WriteLine("rowItem:{0} rowSysRole:{1}",
string.Join(",", both.rowItem.ItemArray),
string.Join(",", both.rowSysRole.ItemArray));
}

Convert DataTable to LINQ: Unable to query multiple fields

Importing a spreadsheet I have filled a DataTable object with that data and returns expected results.
Attempting to put this into a format I can easily query to search for problem records I have done the following
public void Something(DataTable dt)
{
var data = from row in dt.AsEnumerable()
select row["Order"].ToString();
}
Works as expected giving me a list of orders. However I cannot add other fields to this EnumerableRowCollection. Attempting to add other fields as follows gives me an error
public void Something(DataTable dt)
{
// row["Version"] throws an error on me
var data = from row in dt.AsEnumerable()
select row["Order"].ToString(), row["Version"].ToString();
}
Error: "A local variable named 'row' cannot be declared in this scope because it would give a different meaning to 'row' which is already used in a 'child' scope to donate something else"
I'm thinking I need to alias the column name but I'm having no luck. What am I missing here?

It sounds like you're writing a bad select statement. Try the following:
public void Something(DataTable dt)
{
var data = from row in dt.AsEnumerable()
select new {
Order = row["Order"].ToString(),
Something = row["Something"].ToString(),
Customer = row["Customer"].ToString(),
Address = row["Address"].ToString()
};
}
That will create a new collection of Anonymously Typed objects that you can iterate over and use as needed. Keep in mind, though, that you want be able to return data from the function. If you need that functionality, you need to create a concrete type to use (in place of anonymous types).

I think you should use select new like this query for example:
var q = from o in db.Orders
where o.Products.ProductName.StartsWith("Asset") &&
o.PaymentApproved == true
select new { name = o.Contacts.FirstName + " " +
o.Contacts.LastName,
product = o.Products.ProductName,
version = o.Products.Version +
(o.Products.SubVersion * 0.1)
};

You probably want the following.
var data = from row
in dt.AsEnumerable()
select new { Order = row["Order"].ToString(), Version = row["Version"].ToString() };