Nested constructor calls from Dapper

Question

What's the best way to do the following...

conn.Query<Foo>(@"SELECT 1, 2, 'ZEBRA'");

Say Foo has a constructor like so...

public Foo(Bar test, string zebra)

..And Bar has a constructor like this:

public Bar(int one, int two)

This doesn't work, what would be the best approach to achieve the desired result.

`Foo(int first, int second, string derp) : this(new Bar(first, second), derp){}` — , Jun 13 '17 at 13:15

the_joric · Accepted Answer · 2017-06-13T13:10:14.223

2

You could try non-generic Query API (more details are here https://stackoverflow.com/a/8995135/229949):

conn.Query(@"SELECT 1 as one, 2 as two, 'ZEBRA' as zebra")
  .Select(_ => new Foo(new Bar(_.one, _.two), _.zebra);

edited Jun 13 '17 at 13:10

answered Jun 13 '17 at 13:04

the_joric

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score 2 · Answer 2 · answered Jun 13 '17 at 13:11

2

Don't try to hydrate into your real models directly from Dapper if they have constructor requirements like that. Instead, hydrate into a private/internal class, and then instantiate and return the proper models.

internal class FooBarQueryModel 
{
    public string Zebra { get; set; }
    public int One { get; set; }
    public int Two { get; set; }
}

conn.Query<FooBarQueryModel>(sql).Select(qm => new Foo(new Bar(qm.One, qm.Two), qm.Zebra));

answered Jun 13 '17 at 13:11

Graham

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1

would this have some advantage over the 'dynamic' row solution, maybe performance? – Dog Ears Jun 13 '17 at 13:13
1

Anything would be faster than using `dynamic`, even normal reflection. You pay a heavy price for it. – Jonathan Allen Jan 01 '20 at 05:09

Nested constructor calls from Dapper

2 Answers2