Setting up a data relation

Question

I'm new to C# and I'm trying to set up a data relation between a parent and child from an XML data source. I need to find a better explanation of how it is used. Any one know of a good web page or book for an explanation? Anyway this is my specific question: My xml sheet (paraphrased) looks like this: ----------------------------- ABI/Inform Global 0 ... ... ------------------------------ The 'categories' table is a nested table and I want to be able to add and update the categories table in the dataset when the 'database' table is edited or updated. So I have to set up a relation: objRelation = New DataRelation(SOMENAMEHERE objDataSet.Tables[database].Columns[WHATGOESHERE?] objDataSet.Tables[categories].Columns[WHATGOESHERE?]) So this is my question: Based on the XML sheet above what is supposed to go where it says WHATGOESHERE?? And why? I know it's a beginner question right but I'm a beginner. -LJ

dak 0 · Answer

A relation between two tables is always a relation between a colum of each of the two tables. Every row of your child table that has a value X in this column is related to one or more rows of your parent table that has the same value in this column. In your example the parent table would be database. It has the columns name url and description. The child table categories has a column art. But it also needs a column to connect is with the right row in the database table. It seems that the column name could be used for that connection. So these are your tables: [database] name url description [categories] fk_name art The column fk_name must now be related to name: objDataSet.Relations.Add(new DataRelation(SomeRelation objDataSet.Tables[database].Columns[name] objDataSet.Tables[categories].Columns[fk_name])); An exemplary entry in databases would look like this: name url description ---------------------------------------------------------- ABI/Inform Global http://an.url somedescription And the related rows in categories would be: fk_name art ---------------------------- ABI/Inform Global 0 ABI/Inform Global 1 ABI/Inform Global 2 One important thing: to work correctly the name column must only contain unique entries no doubles. In most cases it is better to create an integer column with auto-incrementing (and thus unique) values and use these for relations.