CODEWITHSUNDEEP
c#ado.netreferencedatatable
Superbest
Superbest

Reputation: 26602

Storing references to an object in DataTable using the "this" keyword

I have a collection of objects with no key or order or other obvious index.

I wish to store data regarding each object in a DataTable. I thought an elegant way of doing this would be to store a reference in the owner column, and make that columns type typeof(MyClass).

However, when I try to do this in practice, it doesn't work (it says the primary keys collide). Turns out that putting the instances into a row field just writes "MyProgram.MyClass" into the field - presumably the output of toString even though that row's type was supposed to be MyClass not string.

Here is some sample code which works in LINQPad:

void Main()
{
    // Create a table
    var table = new DataTable();

    var ownerColumn = new DataColumn("Owner", typeof(MyClass));

    var primaryKey = new[] { ownerColumn };

    table.Columns.AddRange(primaryKey);
    table.PrimaryKey = primaryKey;

    table.Columns.Add(new DataColumn("Some Data", typeof(int)) { DefaultValue = 0 });

    // Create 2 objects
    var c1 = new MyClass();
    var c2 = new MyClass();

    // Store their data in the table
    var row = table.NewRow();
    row["Owner"] = c1;
    row["Some Data"] = 1;
    table.Rows.Add(row);

    row = table.NewRow();
    row["Owner"] = c2;
    row["Some Data"] = 2;
    table.Rows.Add(row);
}

// Define other methods and classes here
class MyClass {

}

What do I do to solve this? Do I have to make an id field in MyClass, then use id to fill in the owner column, and then make sure each object receives a unique id at creation myself?

Upvotes: 2

Views: 4535

Answers (2)

Knaģis
Knaģis

Reputation: 21485

You have to implement System.IComparable (non-generic version) interface on MyClass so that DataTable knows how to to compare the value of the column. If this interface is not defined, the code falls back on comparing object.ToString() results.

Upvotes: 2

Damith
Damith

Reputation: 63065

You can use auto increment column :

DataTable dTable = new DataTable();
DataColumn auto = new DataColumn("AutoID", typeof(System.Int32));
dTable.Columns.Add(auto);
auto.AutoIncrement = true;
auto.AutoIncrementSeed = 1;
auto.ReadOnly = true;

Upvotes: 1

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