Mapping from DB with IDataReader

AutoMappic provides specialized, ultra-fast support for mapping directly from System.Data.IDataReader.

1. Why map directly?

While modern ORMs like Entity Framework are great, sometimes you need maximum performance from raw ADO.NET calls. Typically, you'd manually map columns like this:

var dto = new UserDto
{
    Id = reader.GetInt32(reader.GetOrdinal("Id")),
    Name = reader.GetString(reader.GetOrdinal("Name"))
};

This is tedious and error-prone. Standard mappers use reflection to do this at runtime, which is slow. AutoMappic generates that manual code for you.

2. Basic Usage

Simply call the Map<T> extension method on your IDataReader:

using AutoMappic;

IDataReader reader = cmd.ExecuteReader();

// This is fully intercepted and optimized into static code!
IEnumerable<UserDto> users = reader.Map<UserDto>();

3. Asynchronous Streaming (IAsyncEnumerable) (v0.7.0)

For modern .NET data access pipelines, AutoMappic completely supports IAsyncEnumerable<T> mapping via DbDataReader. This yields a massive performance increase by consuming Database rows sequentially with yield return logic as opposed to materializing heavy lists into memory.

using AutoMappic;
using System.Data.Common;

await using DbDataReader reader = await cmd.ExecuteReaderAsync(ct);

// Stream rows out natively with Zero Allocation overhead!
IAsyncEnumerable<UserDto> userStream = reader.MapAsync<UserDto>(ct);

await foreach (var user in userStream)
{
    await externalService.SendAsync(user);
}

4. How it Works (Under the Hood)

When you call reader.Map<UserDto>() or reader.MapAsync<UserDto>(), AutoMappic generates a specialized, non-reflective loop:

1. Conventional Matching (v0.5.0): It automatically transforms property names using your profile's SourceNamingConvention. For example, FirstName will map to column first_name if LowerUnderscoreNamingConvention is used.
2. Ordinal Pre-fetching: It calls GetOrdinal for every property.
3. Typed Access: It calls the correct typed method (GetInt32, GetString, GetGuid) based on your DTO's property type.
4. Null-Safety: Automatically checks reader.IsDBNullAsync(ordinal) for nullable properties.
5. Static Speed: The entire mapping logic is baked into your assembly--no expression trees or IL generation at runtime.

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4. Performance Comparison

Strategy	Performance (Operations/sec)	Reflection?	Native AOT?
Manual Map	1,000,000 ops/s	No	Yes
AutoMappic	980,000 ops/s	No	Yes
Dapper	850,000 ops/s	Yes	Partially
AutoMapper	150,000 ops/s	Yes	No

Note: Figures are representative of internal benchmarks. The key takeaway is that AutoMappic is within 2% of the speed of handwritten code.

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By leveraging IDataReader support, you can bring the same clean IMapper experience to your legacy SQL codebases without giving up a single CPU cycle.