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entity-configuration

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UpdatedJune 25, 2026 at 02:44

Canonical EF Core Fluent API entity configuration rules. Load when creating or modifying IEntityTypeConfiguration classes.

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Ezefeola

Ezefeola/Temper-AI

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SKILL.md

readonly

name	entity-configuration
description	Canonical EF Core Fluent API entity configuration rules. Load when creating or modifying IEntityTypeConfiguration classes.
requires	["backend-dotnet-csharp","dotnet-ddd"]
produces	["entity-configurations","relationship-mappings"]

Entity Configuration — TemperAI

🚨 NON-NEGOTIABLE RULES — ZERO TOLERANCE

NEVER use DataAnnotations on entities
NEVER use nvarchar(max) or varchar(max) — always use explicit lengths from Entity.Rules
NEVER call builder.ToTable() unless a future skill explicitly requires it
NEVER use HasDefaultValueSql() or ValueGeneratedOnAdd() for primary keys
NEVER use OwnsOne in this taxonomy

Load when

Creating IEntityTypeConfiguration<T> classes
Mapping relationships, indexes, precision, or column lengths
Registering configurations in DbContext

Basic entity configuration

public sealed class ProductConfiguration : IEntityTypeConfiguration<Product>
{
    public void Configure(EntityTypeBuilder<Product> builder)
    {
        builder.HasKey(product => product.Id);

        builder.Property(product => product.Name)
            .HasMaxLength(Product.Rules.NAME_MAX_LENGTH)
            .HasColumnType("varchar");

        builder.Property(product => product.Description)
            .HasMaxLength(Product.Rules.DESCRIPTION_MAX_LENGTH)
            .HasColumnType("nvarchar");

        builder.Property(product => product.Price)
            .HasColumnType("decimal(18,2)");

        builder.Property(product => product.Status)
            .HasConversion<string>()
            .HasMaxLength(20)
            .HasColumnType("varchar");

        builder.Property(product => product.CreatedAt)
            .HasColumnType("datetime2");

        builder.Property(product => product.UpdatedAt)
            .HasColumnType("datetime2");

        builder.HasIndex(product => product.Name)
            .IsUnique();
    }
}

Aggregate with child entities

public sealed class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.HasKey(order => order.Id);

        builder.Property(order => order.CustomerId)
            .HasColumnType("uniqueidentifier");

        builder.Property(order => order.Status)
            .HasConversion<string>()
            .HasMaxLength(20)
            .HasColumnType("varchar");

        builder.HasMany(order => order.Items)
            .WithOne()
            .HasForeignKey(item => item.OrderId)
            .OnDelete(DeleteBehavior.Cascade);
    }
}

Column type reference

CLR Type	SQL Type	Notes
`string` ASCII	`varchar(n)`	Codes, names, identifiers
`string` Unicode	`nvarchar(n)`	Descriptions and free text
`decimal`	`decimal(18,2)`	Monetary values
`DateTime`	`datetime2`	Always UTC
`Guid`	`uniqueidentifier`	PKs and FKs
`int`	`int`	Counts and quantities
`bool`	`bit`	Flags
`enum`	`varchar(n)`	Use `.HasConversion<string>()`

Anti-patterns — never do this

// ❌ NEVER use DataAnnotations
public class Product
{
    [Key]
    [Required]
    [MaxLength(100)]
    public Guid Id { get; set; }
}

// ❌ NEVER use nvarchar(max)
builder.Property(product => product.Description)
    .HasColumnType("nvarchar(max)");

// ❌ NEVER use ToTable here
builder.ToTable("Products");

// ❌ NEVER use default SQL generation for PKs here
builder.Property(product => product.Id)
    .HasDefaultValueSql("NEWID()");

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Entity Configuration — TemperAI

🚨 NON-NEGOTIABLE RULES — ZERO TOLERANCE

NEVER use DataAnnotations on entities

NEVER use nvarchar(max) or varchar(max) — always use explicit lengths from Entity.Rules

NEVER call builder.ToTable() unless a future skill explicitly requires it

NEVER use HasDefaultValueSql() or ValueGeneratedOnAdd() for primary keys

NEVER use OwnsOne in this taxonomy

Load when

Creating IEntityTypeConfiguration<T> classes

Mapping relationships, indexes, precision, or column lengths

Registering configurations in DbContext

Basic entity configuration

public sealed class ProductConfiguration : IEntityTypeConfiguration<Product> { public void Configure(EntityTypeBuilder<Product> builder) { builder.HasKey(product => product.Id); builder.Property(product => product.Name) .HasMaxLength(Product.Rules.NAME_MAX_LENGTH) .HasColumnType("varchar"); builder.Property(product => product.Description) .HasMaxLength(Product.Rules.DESCRIPTION_MAX_LENGTH) .HasColumnType("nvarchar"); builder.Property(product => product.Price) .HasColumnType("decimal(18,2)"); builder.Property(product => product.Status) .HasConversion<string>() .HasMaxLength(20) .HasColumnType("varchar"); builder.Property(product => product.CreatedAt) .HasColumnType("datetime2"); builder.Property(product => product.UpdatedAt) .HasColumnType("datetime2"); builder.HasIndex(product => product.Name) .IsUnique(); } }

Aggregate with child entities

public sealed class OrderConfiguration : IEntityTypeConfiguration<Order> { public void Configure(EntityTypeBuilder<Order> builder) { builder.HasKey(order => order.Id); builder.Property(order => order.CustomerId) .HasColumnType("uniqueidentifier"); builder.Property(order => order.Status) .HasConversion<string>() .HasMaxLength(20) .HasColumnType("varchar"); builder.HasMany(order => order.Items) .WithOne() .HasForeignKey(item => item.OrderId) .OnDelete(DeleteBehavior.Cascade); } }

Column type reference

CLR Type

SQL Type

Notes

string ASCII

varchar(n)

Codes, names, identifiers

string Unicode

nvarchar(n)

Descriptions and free text

decimal

decimal(18,2)

Monetary values

DateTime

datetime2

Always UTC

Guid

uniqueidentifier

PKs and FKs

int

Counts and quantities

bool

bit

Flags

enum

varchar(n)

Use .HasConversion<string>()

Anti-patterns — never do this

// ❌ NEVER use DataAnnotations public class Product { [Key] [Required] [MaxLength(100)] public Guid Id { get; set; } } // ❌ NEVER use nvarchar(max) builder.Property(product => product.Description) .HasColumnType("nvarchar(max)"); // ❌ NEVER use ToTable here builder.ToTable("Products"); // ❌ NEVER use default SQL generation for PKs here builder.Property(product => product.Id) .HasDefaultValueSql("NEWID()");