I try to find some references on LINQ with dynamic added strong types, static I have as in example:
var rowColl = _data.AsEnumerable();
var json = (from r in rowColl
select new
{
name = r.Field<string>("name"),
id = r.Field<int>("id"),
}).ToList();
Now where I am interested in if its possible to make "name" and "id" dynamic added on runtime as the information is available in the DataTable "_data", I think there is a simple solution for this however cant find any references on this
It's better practice to avoid using "var" as your type when possible. It looks like rowColl is of type IEnumerable<DataRow>. If that's true, then I would look to see what you can use in the DataRow class (see msdn documentation).
Given that rowColl is actually IEnumerable<DataRow>... If the columns are always going to be in the same order, then you could just do something like r[0] and r[1] in your select statement, i.e.
var json = (from r in rowColl
select new
{
name = r[0], // Where 0 is the index of the "name" column
id = r[1],
}).ToList();
If it complains at you for type-safety, then you could use int.Parse() to cast the string to an int and use the .ToString() extension on your columns instead.
Related
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"));
I want to get list of records from an entity model (I'm using EF version 5) with a particular accountID. I'm being supplied with the tableName string (this has to be dynamic) and the accountID. I'm trying the following 2 methods but none of them is working (giving me errors on the IQueryable object 'table':
PropertyInfo info = _db.GetType().GetProperty(tableName);
IQueryable table = info.GetValue(_db, null) as IQueryable;
var query = table.Where(t => t.AccountID == accID)
.Select(t => t);
List <object> recList = ( from records in table
where records.AccountID == accID
select records).ToList<object>();
The var query = table.Where(....).Select(...) is the correct move as it allows reflection for the query builder at runtime. However, t.AccountID is an error because of the type of t remains unknown.
I've previously used a similar approach in LINQ to SQL, using System.Linq.Expressions.Expression, e.g.:
// NOT TESTED
var table=context.GetTable(dynamicTableName);
var theT=table.Experssion; // actually, I forget. DynamicExpression or MemberBinding? or
var theField=Expression.Field(theT, "AccountID"); // or dynamic name
var query=table.Where(Expression.Equal(theField, accID);
var recList=query.ToList<object>();
If your object has a common interface there is a simpler syntax:
IQueryable<MyInterface> table = context.GetTable("table") as IQueryable<MyInterface>;
var recList=from r in table
where table.AccountID == ac // if your AccountID is on MyInterface
select table;
If you only have a few tables to support, you could do this as well:
IQueryable<MyInterface> table;
if("table1"==tableName)
table=_db.table1
elseif("table2"==tableName)
table=_db.table2
elseif("table3"==tableName)
table=_db.table3
else
throw exception
I built a DynamicRepository for a project I am working on. It uses generic methods exposed through EF along with dynamic linq. It might be helpful to look at that source code here:
https://dynamicmvc.codeplex.com/SourceControl/latest#DynamicMVC/DynamicMVC/Data/DynamicRepository.cs
You can query the entity framework metadata workspace to get the type for a given table name. This link might help:
Get Tables and Relationships
Basically all I'm looking to do is something like the following:
string EntityFrameworkType = "Product";
string searchField = "ProductName";
string searchValue = "My Product";
using( var context = new entitycontext())
{
var result = (from x in context.EntityFrameworkType.Where(l=>l.searchField == searchValue) select x).FirstOrDefault();
}
of course this syntax won't work because context does not contain an entity called "EntityFrameworkType"...
Is it possible to do this another way??? What I'm looking to do in generalize my database duplicate check. In this example, I'm searching for any Product with the Name "My Product". But I'd like to be able to pass in these string for say, ProductCategory with ProductCategoryId = 1.... etc...
you can have a look here to get the idea of how it is done.
You'll need to learn about Expression
I have List where MyType : DynamicObject. The reason for MyType inheriting from DynamicObject, is that I need a type that can contain unknown number of properties.
It all works fine until I need to filter List. Is there a way I can do a linq that will do something like this:
return all items where any of the properties is empty string or white space?
(from the comment) can I do above linq query with List?
Yes, here is how you can do it with ExpandoObject:
var list = new List<ExpandoObject>();
dynamic e1 = new ExpandoObject();
e1.a = null;
e1.b = "";
dynamic e2 = new ExpandoObject();
e2.x = "xxx";
e2.y = 123;
list.Add(e1);
list.Add(e2);
var res = list.Where(
item => item.Any(p => p.Value == null || (p.Value is string && string.IsNullOrEmpty((string)p.Value)))
);
The ExpandoObject presents an interface that lets you enumerate its property-value pairs as if they were in a dictionary, making the process of checking them a lot simpler.
Well as long as each object's properties are not unknown internally to themselves you could do it.
There isn't a great generic way to test all the properties of a dynamic object, if you don't have control over the DynamicObject you hope the implementer implemented GetDynamicMemberNames() and you can use the nuget package ImpromptuInterface's methods for getting the property names and dynamically invoking those names.
return allItems.Where(x=> Impromptu.GetMemberNames(x, dynamicOnly:true)
.Any(y=>String.IsNullOrWhiteSpace(Impromptu.InvokeGet(x,y));
Otherwise, since it's your own type MyType you can add your own method that can see internal accounting for those member values.
return allItems.Where(x => x.MyValues.Any(y=>String.IsNullOrWhitespace(x));
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;