Map a column with string representing a list to a List<> object using Dapper

Question

Map a column with string representing a list to a List<> object using Dapper

dapper dapper-extensions sql-server string-split

Question

I have the following model:

public class Model {
   public string Name { get; set; }
   public List<int> Numbers { get; set; }
}

And an SQL query that returns the following dataset containing two nvarchar columns:

 Name |  Numbers
'foo' | '1,2,3,4'
'bar' | '4,17'

Is there a simple way to auto-assign the results of the query to a List<Model> using Dapper?

I know I could use multi-mapping and make the splitting myself in C# code, but I would rather get a simpler solution.

Mugen

Popular Answer

An alternative option with multimapping... pretty ugly

public class Result
{
    public string Name { get; set; }
    public List<int> NumberList { get; set; }
    public string Numbers { set { NumberList = value.Split(',').Select(Int32.Parse).ToList(); } }
}

public class DapperTests
{
    [Test]
    public void Test()
    {
        var conn = new SqlConnection(@"Data Source=.\sqlexpress; Integrated Security=true; Initial Catalog=mydb");

        conn.Open();

        var sql = @"
            select Name = 'Foo', Numbers = '1,2,3';
            select Name = 'Bar', Numbers = '4,5,6';";

        var expectedResults = 2;

        var results = new List<Result>();
        using (var multi = conn.QueryMultiple(sql))
        {
            for (int i = 0; i < expectedResults; i++)
            {
                results.Add(multi.Read<Result>().Single());
            }
        }

        Assert.That(results.Count, Is.EqualTo(2));

        Assert.That(results.FirstOrDefault(x => x.Name == "Foo").NumberList.Count, Is.GreaterThan(0));
        Assert.That(results.FirstOrDefault(x => x.Name == "Bar").NumberList.Count, Is.GreaterThan(0));
    }
}

Matt McCabe

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Accepted Answer

I'm not sure if you can call this "simpler", but something like this is an option:

public class Result
{
    public string Name { get; set; }
    public List<int> Numbers { get; set; }
}
public class DapperTests
{
    [Test]
    public void Test()
    {
        var conn = new SqlConnection(@"Data Source=.\sqlexpress; Integrated Security=true; Initial Catalog=mydb");

        conn.Open();

        var result = conn.Query<string, string, Result>(
                    "select Name = 'Foo', Numbers = '1,2,3' union all select Name = 'Bar', Numbers = '4,5,6'", (a, b) => new Result
                    {
                        Name = a,
                        Numbers = b.Split(',').Select(Int32.Parse).ToList()
                    }, splitOn: "*").ToList();

        Assert.That(result.Count, Is.EqualTo(2));
        Assert.That(result.FirstOrDefault(x => x.Name == "Foo").Numbers.Count, Is.GreaterThan(0));
        Assert.That(result.FirstOrDefault(x => x.Name == "Bar").Numbers.Count, Is.GreaterThan(0));
    }
}

Map a column with string representing a list to a List<> object using Dapper

Question

Accepted Answer

Popular Answer

Performance

Expression Evaluator