Tutorials ADO.NET Core Tutorial
DTO Mapping — Complete Guide
DTO Mapping — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of ADO.NET Core Tutorial on Toolliyo Academy.
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ADO.NET Core Tutorial · Lesson 57 of 100
DTO Mapping
Foundations ✓ → SQL & safety ✓ → Production → Projects
Production · 3 — ASP.NET & enterprise · ~10 min · Module 6: ASP.NET Core Integration
What is this?
Map SqlDataReader columns to DTOs manually or with light helpers — keep DTOs API-shaped.
Why should you care?
ShopNest should not leak raw DataRow shapes to clients.
See it live — copy this example
Use a .NET console or API project with SQL Server LocalDB. Run dotnet run after pasting.
sealed record OrderDto(int Id, decimal Total, string Status);
static OrderDto Map(SqlDataReader r) => new(
r.GetInt32(r.GetOrdinal("Id")),
r.GetDecimal(r.GetOrdinal("Total")),
r.GetString(r.GetOrdinal("Status")));What happened?
- Ordinals once per shape.
- Handle nulls.
- Don’t over-automap huge graphs blindly.
Practice next
- Write Map helper.
- Use in reader loop.
- Add nullable CustomerName.
- Map CreatedAt.
- Ignore unused columns.
Remember
Reader → DTO. Handle nulls. Stable contracts.
ShopNest OrderDto map
API returns OrderDto only.
Outcome: Clients insulated from SQL renames via mapping.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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