Mapping

Db4Net uses standard .NET mapping attributes.

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

[Table("app_users")]
public sealed class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    [Column("display_name")]
    public string Name { get; set; } = "";

    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime UpdatedAt { get; set; }

    [NotMapped]
    public string DisplayOnly { get; set; } = "";
}

Typed projections alias mapped columns so Dapper can map results back to property names:

SELECT [Id], [display_name] AS [Name] FROM [app_users]

Keys

[Key] and the Id / <TypeName>Id convention are used by:

• Update(entity) and UpdateMany(entities)
• Delete(entity) and DeleteMany(entities)
• WhereKey(entity)
• default conflict targets for conflict-aware inserts

Key metadata identifies mapped columns for equality predicates, conflict targets, and explicit single-row insert key terminals. It does not imply entity tracking, automatic entity mutation, relationship identity maps, or automatic concurrency behavior.

Conflict-aware inserts use all key columns by default, including composite [Key] metadata. Entity update/delete conveniences and many update/delete conveniences require a single key column and a non-default key value.

Generated and Ignored Members

[NotMapped] members are excluded from SelectFrom<T>() and rejected in typed selectors such as Select, Where, OrderBy, Value, and Set.

[Key] and [DatabaseGenerated(...)] are independent. A [Key] column can also be [DatabaseGenerated(DatabaseGeneratedOption.Identity)]: Db4Net still uses it in WHERE predicates for entity updates and deletes, and it can be returned by explicit single-row insert key terminals, but Db4Net omits it from automatic insert values because the database generates it.

[DatabaseGenerated(DatabaseGeneratedOption.Identity)] and [DatabaseGenerated(DatabaseGeneratedOption.Computed)] mapped properties are omitted by Values(entity), Insert(entity), InsertMany(entities), and conflict-aware insert values. Database-generated non-key properties are also omitted from entity-driven update assignments in Update(entity) and UpdateMany(entities). Explicit .Value(...) and .Set(...) calls remain caller-controlled.

Database-generated members cannot be used as default or explicit conflict targets, and cannot be selected through InsertOrUpdate.Update(...). Conflict target columns also cannot be selected through InsertOrUpdate.Update(...).

Generated key readback is explicit and limited to regular single-row insert terminals such as Insert(entity).ExecuteReturnKey<TResult>() and InsertInto<T>().Values(entity).ReturnKey(...).Execute<TResult>(). Db4Net does not mutate entity instances after insert or refresh all computed values.