how can I get all Columns of a tabel via dynamic linq? Is there something like wildcards? For example:
var query = db.myTable.select("*").orderby("Name"); or
var query = db.myTable.select("new { * }").orderby("Name");
and how can I convert the query to a List?
ar query = db.myTable.select("new { * }").orderby("Name").toList();
Thanks
Related
Sql query to LINQ: Both are pasted over here, getting issue in LINQ - need suggestion:
select bm.MachineId,al.AlarmId,am.AlarmName, count(al.AlarmId)AlarmCount
from BatchMachineWise bm
join AlarmLog al on bm.MachineId = al.MachineId
join Alarm am on am.AlarmId = al.AlarmId
where bm.BatchId = 12476
group by bm.MachineId,al.AlarmId,am.AlarmName
GroupBy returns IGrouping<TKey,TElement> interface which has Key property which should be used to access fields used for grouping:
select new AlarmSummary
{
MachineId = gr.Key.MachineId,
AlarmId = gr.Key.AlarmId,
AlarmName = gr.Key.AlarmName
....
}
Suppose my datatable is filled with data.
After filling data can we again put some condition on datatable with linq to extract data.
Suppose my datatable has 10 employee record.
So can we extract only those employee whose salary is greater than 5000 with linq query.
I know that we can achieve it datatable.select(). How can you achieve this with linq?
You can get a filtered set of rows, yes:
var query = table.AsEnumerable()
.Where(row => row.Field<decimal>("salary") > 5000m);
This uses the AsEnumerable and Field extension methods in DataTableExtensions and DataRowExtensions respectively.
Try this:
var query = (from t0 in dtDataTable.AsEnumerable()
where t0.Field<string>("FieldName") == Filter
select new
{
FieldName = t0.Field<string>("FieldName"),
FieldName2 = t0.Field<string>("FieldName2"),
});
Let's ay I have this query:
var results = from row in db.Table select row;
How can I access this:
string name = results[0]["columnName"];
if you really want a particular index you can use the Skip() method with First().
var rowOffset = 0;
var results = (from row in db.Table
select row).Skip(rowOffset).First()["columnName"];
But unless you are using a Where clause I would really recommend using the indexer. The indexer is pretty much a direct reference while the LINQ statement would be using the objects iterator.
Also don't forget you can do much more advanced stuff with LINQ.
var rowOffset = 0;
var pageLength = 10;
var results = (from row in db.Table
let colValue = row["columnname"]
where colValue != null
select colValue.ToString()
).Skip(rowOffset)
.Take(pageLength)
.ToArray();
var commaString = string.Join(", ", results);
If you specifically just want the zeroth element, you can use results.First()
results is a IEnumerable list of Rows. So you can get it with a simple foreach.
foreach(var row in results)
{
string name = row["columnName"];
}
(from row in db.Table select row).First().columnName
What do I put in my order by?? I want to order by Name. I have moved the orderby after the distinct because I read that it needs to be done last.
var result = (from r in db.RecordDocs
where r.RecordID == recordID
select new
{
DocTypeID = r.Document.DocType.DocTypeID,
Name = r.Document.DocType.Name,
Number = r.Document.DocType.Number
}
).Distinct().OrderBy( );
Just do
.OrderBy(doc => doc.Name)
Another option, if you really prefer the query expression syntax would be to chain your query construction across multiple statements:
var query = from r in db.RecordDocs
where r.RecordID == recordID
select new
{
DocTypeID = r.Document.DocType.DocTypeID,
Name = r.Document.DocType.Name,
Number = r.Document.DocType.Number
};
query = query.Disctinct();
query = from doc in query orderby doc.Name select doc;
Since all of these methods are deferred, this will result in the exact same execution performance.
Is there a pattern using Linq to dynamically create a filter?
I have the need to create custom filtering on a list, in the past I would just dynamically create the SQL...it doesn't seem like this is possible with Linq.
Check out the Dynamic Linq Library from ScottGu's blog:
For example, below is a standard type-safe LINQ to SQL VB query that retrieves data from a Northwind database and displays it in a ASP.NET GridView control:
Dim Northwind As New NorthwindDataContext
Dim query = From q In Northwind.Products Where p.CategoryID = 2 And p.UnitPrice > 3 Order By p.SupplierID Select p
Gridview1.DataSource = query
GridView1.DataBind()
Using the LINQ DynamicQuery library I could re-write the above query expression instead like so
Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products .where("CategoryID=2 And UnitPrice>3") . OrderBy("SupplierId")
Gridview1.DataSource = query
GridView1.DataBind()
Notice how the conditional-where clause and sort-orderby clause now take string expressions instead of code expressions. Because they are late-bound strings I can dynamically construct them. For example: I could provide UI to an end-user business analyst using my application that enables them to construct queries on their own (including arbitrary conditional clauses).
Dynamic Linq is one way to go.
It may be overkill for your scenario. Consider:
IQueryable<Customer> query = db.Customers;
if (searchingByName)
{
query = query.Where(c => c.Name.StartsWith(someletters));
}
if (searchingById)
{
query = query.Where(c => c.Id == Id);
}
if (searchingByDonuts)
{
query = query.Where(c => c.Donuts.Any(d => !d.IsEaten));
}
query = query.OrderBy(c => c.Name);
List<Customer> = query.Take(10).ToList();
Dynamically Composing Expression Predicates
something like this?
var myList = new List<string> { "a","b","c" };
var items = from item in db.Items
where myList.Contains(item.Name)
select item;
that would create a sql statement like
SELECT * FROM Items [t0] where Name IN ('a','b','c')