使用NPoco 3的嵌套对象映射

Question

I'm trying to get a nested mapping running but the nested object is null. Which means in my case result[0].Location is null. I'm using NPoco 3.3.0-beta3 together with Postgres.

Here the code snippet:

var db = new Database(new NpgsqlConnection(configurations["ConnectionStrings:Database"]));

var sql = Sql.Builder
    .Append("SELECT r.*, l.* FROM race r")
    .Append("INNER JOIN location l ON r.location_id = l.id");

using (db.Connection)
{
    db.Connection.Open();
    var result = Db.Fetch<RaceEntity>(sql);
    // result[0].Location == null
}

RaceEntity:

[TableName("race")]
[PrimaryKey("id", AutoIncrement = true)]
public class RaceEntity
{
    [Column("id")]
    public int Id { get; set; }

    [Column("name")]
    public string Name { get; set; }

    [Column("location_id")]
    public int LocationId { get; set; }

    [Column("date")]
    public DateTime Date { get; set; }

    [ResultColumn]
    public LocationEntity Location { get; set; }
}

LocationEntity

[TableName("location")]
[PrimaryKey("id", AutoIncrement = true)]
public class LocationEntity
{
    [Column("id")]
    public int Id { get; set; }

    [Column("name")]
    public string Name { get; set; }

    [Column("province")]
    public string Province { get; set; }

    [Column("postal")]
    public string Postal { get; set; }

    [Column("country")]
    public string Country { get; set; }

    [Column("iso_code")]
    public string IsoCode { get; set; }
}

Race Table

CREATE TABLE "race" (
    "id" SERIAL PRIMARY KEY,
    "name" VARCHAR(100) NOT NULL,   
    "location_id" INTEGER REFERENCES "location" (id),
    "date" date NOT NULL
);

Location Table

CREATE TABLE "location" (
    "id" SERIAL PRIMARY KEY,
    "name" VARCHAR(100) NOT NULL,
    "province" VARCHAR(100) NULL DEFAULT NULL,
    "postal" VARCHAR(30) NULL DEFAULT NULL,
    "country" VARCHAR(70) NOT NULL,
    "iso_code" VARCHAR(10) NULL DEFAULT NULL
);

Answer 1

Remove attribute [ResultColumn] from Location property. Location property is not a column in the database and does not therefore require the attribute.

Even if the property was a column in the database, you would require to note the following from NPoco wiki

Note: These columns will need to be explicitly specified in the SQL. It will not be included in the auto generated SQL.