Source generators

CaeriusNet includes source generators for DTO mappers and table-valued parameter mappers. They remove repetitive mapping code while keeping the mapping contract visible in your C# types.

You do not install a separate analyzer or generator package. The generators are included with the CaeriusNet NuGet package.

dotnet add package CaeriusNet

When to use source generators

Use source generators when you want CaeriusNet to create mapper implementations from simple record or class definitions.

Attribute	Use it for	Generated contract
[GenerateDto]	Stored procedure result rows	ISpMapper<T>
[GenerateTvp]	SQL Server table-valued parameter rows	ITvpMapper<T>

The generator output is compile-time code. There is no runtime reflection or runtime mapper discovery.

DTO mapper generation

Use [GenerateDto] on a sealed partial record or class with a primary constructor. Constructor parameters map to result-set columns by ordinal position.

using CaeriusNet.Attributes.Dto;

[GenerateDto]
public sealed partial record UserDto(int Id, string Name, byte Age);

The stored procedure must return columns in the same order:

SELECT Id, Name, Age
FROM dbo.Users
ORDER BY Id;

Requirements

• The type must be sealed.
• The type must be partial.
• The type must have a primary constructor.
• Constructor parameter order must match the stored procedure result-set order.

If a requirement is not met, the analyzer reports a build diagnostic. See Diagnostic rules.

Nullable columns

Use nullable C# types for columns that can return NULL.

[GenerateDto]
public sealed partial record ProductDto(
    int Id,
    string Name,
    string? Description,
    int? Stock);

The generated mapper checks IsDBNull before reading nullable values.

Supported common types

C# type	Typical SQL Server type
bool	bit
byte	tinyint
short	smallint
int	int
long	bigint
decimal	decimal
float	real
double	float
string	nvarchar
DateTime	datetime2
DateOnly	date
TimeOnly	time
DateTimeOffset	datetimeoffset
TimeSpan	time
Guid	uniqueidentifier
byte[]	varbinary
Enums	The enum underlying type

For unsupported types, the analyzer reports a diagnostic so you can choose a safer DTO shape.

TVP mapper generation

Use [GenerateTvp] on a sealed partial record or class. The constructor parameters define the TVP row shape.

using CaeriusNet.Attributes.Tvp;

[GenerateTvp(Schema = "dbo", TvpName = "tvp_UserId")]
public sealed partial record UserIdTvp(int Id);

The SQL type must match the C# constructor order and compatible SQL types:

CREATE TYPE dbo.tvp_UserId AS TABLE
(
    Id INT NOT NULL
);

Use the generated TVP with AddTvpParameter.

var ids = userIds.Select(id => new UserIdTvp(id));

var sp = new StoredProcedureParametersBuilder("dbo", "sp_GetUsers_By_Ids", 256)
    .AddTvpParameter("Ids", ids)
    .Build();

TVP requirements

• Schema must match the SQL Server type schema.
• TvpName must match the SQL Server type name.
• Constructor parameter order must match the SQL type column order.
• Nullable C# parameters should match nullable SQL columns.
• The input collection must contain at least one row.

Manual mapper comparison

You can still write mappers manually when you need full control.

Task	Generated mapper	Manual mapper
DTO row mapping	Add [GenerateDto] to a DTO	Implement ISpMapper<T>
TVP row mapping	Add [GenerateTvp] to a TVP row type	Implement ITvpMapper<T>
Contract validation	Analyzer diagnostics at build time	Your tests and runtime behavior
Boilerplate	Minimal	You write every reader or TVP call

Inspect generated files

If you need to troubleshoot generated output, enable compiler-generated files in your project.

<PropertyGroup>
  <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
  <CompilerGeneratedFilesOutputPath>obj\Generated</CompilerGeneratedFilesOutputPath>
</PropertyGroup>

You usually do not need this setting. It is useful when you are diagnosing a mapper issue or reviewing what code is compiled.

Related content

• DTO mapping
• Table-valued parameters
• Compiler diagnostics
• Diagnostic rules