Dapper get error when Join between tables

Question

Dapper get error when Join between tables

asp.net asp.net-core asp.net-core-1.0 dapper dapper-extensions

Question

I'm new to dapper i get error when i retrieve data from joined table

var qry = @"SELECT Cities.Id,
                           Cities.Name,
                           Cities.Sort,
                           Countries.Name
                           FROM[dbo].[Cities]
                            JOIN Countries ON Countries.Id = Cities.CountryId";

var result = con.Query<Cities, Countries>(qry);

this is the error message

'SqlConnection' does not contain a definition for 'Query' and no extension method 'Query' accepting a first argument of type 'SqlConnection' could be found (are you missing a using directive or an assembly reference?)

Error Image

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Wiktor Zychla · Accepted Answer · 9/5/2016 9:51:39 AM

The error is caused by invalid invocation - there is no overload that accepts two generic arguments.

Event though Dapper supports multimapping, the call actually requires three generic arguments, TFirst, TSecond and TReturn (where TReturn can be one of the two or yet another type).

https://github.com/StackExchange/dapper-dot-net#multi-mapping

An example valid call from the docs

var data = connection.Query<Post, User, Post>(sql, (post, user) => { post.Owner = user; return post;});

An invalid invocation with only two generic arguments yields exactly the error message you get.

My guess is you either wanted the 3rd overload that accepts a single generic argument

 Query<TResult>( string sql, Type[] types, Func<object[], TResult> map, ... );

or the 4th one that accepts three

 Query<TFirst, TSecond, TResult>( string sql, Func<TFirst, TSecond, TResult> map, ... );

In both cases you still need a map function.

Dapper get error when Join between tables

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