CODEWITHSUNDEEP
c#dappernpgsql
CoolMcGrrr
CoolMcGrrr

Reputation: 774

Dapper, Postgres and camelcase

I'm trying to use Dapper with Postgres and for the life of me I can't get the column mapping to work. I'm using camel_casing for columns in the database.

This is the table I'm working with:

create table test_table
(
    id uuid default gen_random_uuid() not null
        constraint test_table_pk
            primary key,
    first_name varchar(256) not null,
    created_date timestamp not null
);

alter table test_table owner to root;

I have made the following application to recreate the issue

namespace DapperIssue {
    class Program {
        static void Main(string[] args) {
            NpgsqlConnection.GlobalTypeMapper.UseNodaTime();
            DefaultTypeMap.MatchNamesWithUnderscores = true;
            
            using (var conn =
                new NpgsqlConnection("CONNECTIONSTRING FOR DATABASE")) {
                
                conn.Open();
                var result = conn.Query<T1>(@"
SELECT id, first_name FROM test_table", new { });

                var result2 = conn.Query<T2>(@"
SELECT id, first_name, created_date FROM test_table", new { });
            }
        }
    }

    //public record T1(Guid Id, string FirstName) { }
    
    public class T1 {
        public Guid Id { get; }
        public string FirstName { get; }

        public T1(Guid id, string firstName) {
            Id = id;
            FirstName = firstName;
        }
    }

    public record T2(Guid Id, string FirstName, Instant CreateDate) {
    }
}

The application is failing when trying to query the database with the following error:

System.InvalidOperationException: A parameterless default constructor or one matching signature (System.Guid id, System.String first_name)

My understanding was that setting DefaultTypeMap.MatchNamesWithUnderscores = true should make this work.

Using Dapper "2.0.78" and NpgSql "5.0.3"

Upvotes: 2

Views: 3206

Answers (1)

Jehof
Jehof

Reputation: 35544

This seems to be an open issue in dapper. Read more DefaultTypeMap.MatchNamesWithUnderscores is ignored for ctor parameters and Added support for MatchNamesWithUnderscores and ctor parameters.

Adding a parameterless constructor should fix your problem. The columns should be mapped to the properties of the class with the named setting.

Upvotes: 1

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