子级为IEnumerable的Dapper查询对象

Question

I am trying query all countries and in each country object it would fill up the provinces.

I have the following Classes

public class Country
{
    public int Countryid { get; set; }
    public string CountryName { get; set; }

    public IEnumerable<Province> Provinces { get; set; }
}

public class Province
{
    public int ProvinceId { get; set; }
    public string ProvinceName { get; set; }
}

public IEnumerable<Country> GetCountries()
{
    var query = @"
          SELECT [Country].[CountryId], [Country].[Name] as CountryName, [Province].[ProvinceId], [Province].[Name] as ProvinceName
          FROM [Province]
            RIGHT OUTER JOIN [Country] ON [Province].[CountryId] = [Country].[CountryId]
          WHERE [Country].[CountryId] > 0";

    return _connection.Query<Country, Province, Country>(query, (country, province) =>
    {
        country.Provinces = country.Provinces.Concat(new List<Province> { province });
        return country;
    }, null);
}

The error that I get is the following:

System.ArgumentException: 'When using the multi-mapping APIs ensure you set the splitOn param if you have keys other than Id Parameter name: splitOn'

I have been following this example:

https://gist.github.com/Lobstrosity/1133111

From my perspective, I don't see what I did much different besides mine being an outer join which I think should not matter, the result format is about the same.

Why do I need the split on and can this work without it?

Answer 1

IIRC, I did something like this.

 var query = @"
          SELECT [Country].[CountryId], [Country].[Name] as CountryName, [Province].[ProvinceId], [Province].[Name] as ProvinceName
          FROM [Province]
            RIGHT OUTER JOIN [Country] ON [Province].[CountryId] = [Country].[CountryId]
          WHERE [Country].[CountryId] > 0";

    List<Country> countries = new List<Country>();      

    _connection.Query<Country, Province, Country>(query, (country, province) =>
    {           
        Country lastCountry = countries.FirstOrDefault(d => d.CountryId == country.Id);
        if(lastCountry == null)
        {
            countries.Add(country);
            lastCountry = country;

        }
        lastCountry.Provinces = lastCountry.Provinces.Concat(new List<Province> { province });
        return lastCountry;
    }, null);

    return countries;

I typed this out in LinqPad, so you will need to debug and check it is correct, been a long time since I used Dapper in anger