Question

I’m looking for a way to fix and/or abstract away a comma-separated values (CSV) list in a database field in order to reconstruct a usable relationship such that I can properly join the two tables below and query them using C# LINQ and its .Join method.

Following is a sample showing the Person table and CsvArticleIds field having a CSV value to represent a one-to-many association with Article records.

TABLE [dbo].[Person]

Id Name       CsvArticleIds
-- ---------- --------
1  Joe        "15,22"
5  Ed         "22"
10 Arnie      "8,15,22"

^^^(Of course a link table should have been created; nonetheless the relationship with articles is trapped inside that list of CSV values.)

TABLE [dbo].[Article]

Id Title
-- ----------
8  Beginning C#
15 A Historic look at Programming in the 90s
22 Gardening in January

Additional Info

• the fix can be at any level: C#.NET or SQL Server
• something easy because I will be repeating the solution for many other CSV values in other tables.
• Elegant is nice too.
• not looking for efficiency because this is part of a one-time data migration task and can take as long as it wants to run.

Answer 1

transform the Person table into something more useful first, like

var newpersons =
    data.Persons.Select(p => new
        {
          Id = p.Id,
          Name = p.Name,
          ArticleIds = p.CsvArticleIds.Substring(1, p.CsvArticleIds.Length -2).Split(',').ToList()
        });

now you can join against the person.ArticleIds collection.

if holding the entire transformed Person table in memory can’t be done, then use the same .Select to transform groups of records, pulling Person objects out of the DB, say 100 at a time, using Skip() and Take().