Binding LINQ query to DataGridView - linq

This is very confusing, I use AsDataView to bind query result to a dgv and it works fine with the following:
var query = from c in myDatabaseDataSet.Diamond where c.p_Id == p_Id select c;
dataGridView1.DataSource = query.AsDataView();
However, this one results in an Error:
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
};
dataGridView1.DataSource = query.AsDataView();
Error:
Instance argument: cannot convert from
'System.Collections.Generic.IEnumerable<AnonymousType#1>' to
'System.Data.DataTable'
AsDataView doesn't show up in query.(List). Why is this happen? How to bind the query above to the dgv then?.

The signature of the AsDataView is as follows:
public static DataView AsDataView(
this DataTable table
)
The only parameter is the DataTable.
The query you have is returning an IEnumerable of an anonymous type which doesn't have an implicit conversion to a DataTable (or a sequence of DataRow instances, in which case you could use that to help you create a DataTable).
You need to get the results back into a DataTable or something you can convert into a DataTable and then it will work.
In your particular case, it seems that you were (or are) using typed DataSets. If that is the case, then you should be able to take the values that were selected and then create new typed DataRow instances (there should be factory methods for you) which can then be put into a typed DataTable, which AsDataView can be called on.

just simply convert the result to a list and bind it to your grid.
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
}.ToList();
dataGridView1.DataSource = query;

Related

Dynamic Linq on DataTable error: no Field or Property in DataRow, c#

I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));

LINQ Select with multiple tables fields being writeable

I'm new to LINQ and I'm doing pretty well until now, but now stuck with this.
I've a LINQ object bounded to a DataGridView to let the user edit is contains.
for simple one table query, it go fine, but how to build a LINQ query with multiple table, so the result will still be read/write?
Here a example of what I mean:
GMR.Data.GMR_Entities GMR = new GMR.Data.GMR_Entities();
var dt = from Msg in GMR.tblMessages
join lang in GMR.tblDomVals on 1 equals 1//on Msg.pLangueID equals lang.ID
select Msg;
// select new {lang.DescrFr, Msg.Message,Msg.pLangueID } ;
this.dataGridView1.DataSource = dt;
In this simple query, if I return only "Msg" with the select statement, the grid can be edited. But if I replace the select statement with select new {lang.DescrFr, Msg.Message,Msg.pLangueID } ; the grid will be readable only.
I can easily understand that this is due because the query result is a anonymous type.
But is there a way to let the table tblMessage being writable?
try creating your own class, for example
public class MsgLangInfo
{
public string langDescFr{get;set;}
public int pLangueID{get;set;}
}
And at the select statement create an object of this class with new like below
select new MsgLangInfo {
langDescFr = lang.DescrFr,
langDescFr = Msg.Message,Msg.pLangueID
} ;
This way you can avoid the anonymous type problem.
You need to select the originals rows and explicitly set the grid columns.

Using .Contains within a linq query returning a SystemException

I am having some trouble with a linq query I am trying to write.
I have List A of products that have been modified so I am trying to get the list of products from the db to allow me to apply the changes to them.
I have tried 2 different queries
var query = from p in db.Products
where products.Select(z => z.id).Contains(p.Id)
select p;
var query2 = from p in db.Products where (from o in products
select o.id)
.Contains(p.Id)
select p;
Both attempts are returning an error
base {System.SystemException} = {"Unable to create a constant value of type 'ProjectABC.Models.ProductModel'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."}
What am I doing wrong?
I had the same problem the other day, seems EF doesn't support Select().Contains() without giving that error. After testing around for a bit, I ended up splitting it up in what in your case would correspond to;
var IDs = products.Select(z=>z.id);
var query = from p in db.Products
where IDs.Contains(p.Id)
select p;
which worked well in my case when the "products" collection was in memory anyway (ie a ToList()'ed result from the database)

Can we filter Datatable with LINQ?

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"),
});

Building Dynamic LINQ Queries based on Combobox Value

I have a combo box in Silverlight. It has a collection of values built out of the properties of one of my LINQ-to-SQL objects (ie Name, Address, Age, etc...). I would like to filter my results based off the value selected in a combo box.
Example: Say I want everyone with a last name "Smith". I'd select 'Last Name' from the drop down list and enter smith into a textbox control. Normally I would write a LINQ query similar to...
var query = from p in collection where p.LastName == textbox.Text select p;
Is it possible to decide the property dynamically, maybe using Reflection? Something like
var query = from p in collection where p.(DropDownValue) == textbox.Text select p;
Assuming:
public class Person
{
public string LastName { get; set; }
}
IQueryable<Person> collection;
your query:
var query =
from p in collection
where p.LastName == textBox.Text
select p;
means the same as:
var query = collection.Where(p => p.LastName == textBox.Text);
which the compiler translates from an extension method to:
var query = Queryable.Where(collection, p => p.LastName == textBox.Text);
The second parameter of Queryable.Where is an Expression<Func<Person, bool>>. The compiler understands the Expression<> type and generates code to build an expression tree representing the lambda:
using System.Linq.Expressions;
var query = Queryable.Where(
collection,
Expression.Lambda<Func<Person, bool>>(
Expression.Equal(
Expression.MakeMemberAccess(
Expression.Parameter(typeof(Person), "p"),
typeof(Person).GetProperty("LastName")),
Expression.MakeMemberAccess(
Expression.Constant(textBox),
typeof(TextBox).GetProperty("Text"))),
Expression.Parameter(typeof(Person), "p"));
That is what the query syntax means.
You are free to call these methods yourself. To change the compared property, replace this:
typeof(Person).GetProperty("LastName")
with:
typeof(Person).GetProperty(dropDown.SelectedValue);
Scott Guthrie has a short series on dyamically built LINQ to SQL queries:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
That's the easy way...then there's another way that's a bit more involved:
http://www.albahari.com/nutshell/predicatebuilder.aspx
You can also use the library I created: http://tomasp.net/blog/dynamic-linq-queries.aspx. You would store the properties in ComboBox as lambda expressions and then just write:
var f = (Expression<Func<Product, string>>)comboBox.SelectedValue;
var query =
from p in collection
where f.Expand(textBox.Text)
select p;

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