Dapper unlimited multi-mapping

Question

So I have a situation where I have to join (and map) more than 7 entities (which as far as I see is the current limitation of Dapper). This is what I've got so far (pseudo code):

using (var connection = new SqlConnection(_connectionString)) {
   IEnumerable<BigEntity> results = 
      connection.Query<BigEntity, Lookup1, Lookup2, ... around 10 of them>(sql, 
         (b, l1, l2, l3) => {
            // map and return here
         },
         splitOn: "split1, split2 ...");
}

Is there any way around this limitation ? Anyone faced this before ? Some Dapper extensions perhaps ?

@talles, nope it's not that hard, you're right. However I'd like to have it official and not have my own patched up version of Dapper. — Dimitar Dimitrov, Dec 19 '13 at 06:47
Any updates on this concern? We are hitting the same issue :-( ~Hejo — , Feb 15 '17 at 11:12
@Hejo If it helps, I ended up adding a new (wrapper) POCO with all the fields I need and mapped to it. — Dimitar Dimitrov, Feb 15 '17 at 11:15

Hejo · Accepted Answer · 2017-02-15T12:39:09.980

There is a merged PR on this topic from Sep 2014:

https://github.com/StackExchange/Dapper/pull/158/files

The PR added methods where you can pass an array of Types. So the limitation to 7 entities does not exist anymore on these methods.

This is a Code Test from the Dapper Repo showing how to use one of these new methods:

public async Task TestMultiMapArbitraryWithSplitAsync()
    {
        const string sql = @"select 1 as id, 'abc' as name, 2 as id, 'def' as name";
        var productQuery = await connection.QueryAsync<Product>(sql, new[] { typeof(Product), typeof(Category) }, (objects) => {
            var prod = (Product)objects[0];
            prod.Category = (Category)objects[1];
            return prod;
        });

        var product = productQuery.First();
        // assertions
        product.Id.IsEqualTo(1);
        product.Name.IsEqualTo("abc");
        product.Category.Id.IsEqualTo(2);
        product.Category.Name.IsEqualTo("def");
    }

score 6 · Answer 2 · edited Dec 19 '13 at 06:26

6

Currently the only two ways that I know of to work around this is to

Create a POCO class with the fields you want and use your query like a table
Modify Dapper's source code to allow for more mappings.

edited Dec 19 '13 at 06:26

Sergey Berezovskiy

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answered Dec 15 '13 at 15:04

mosesfetters

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I appreciate your response +1. However, with a risk of sounding like a jerk, this is not much of an answer. The whole reason I'm asking the question is so that I don't have to *modify* Dapper or create a wrapper POCO. Cheers. – Dimitar Dimitrov Dec 19 '13 at 10:27
1

Completely understandable :) I should probably have prefaced this and said that I did a ton of research into this and others have had similar issues and its a hard limit in the system and people have made pull requests requesting this exact feature. I could not find anything like what you are looking for when I needed it for a requirement. Sorry. – mosesfetters Dec 19 '13 at 13:29

Dapper unlimited multi-mapping

2 Answers2