dotnet/efcore · error · InvalidOperationException

Entity type ' ' has a split mapping for ' ', but it also…

Error message

Entity type '{entityType}' has a split mapping for '{storeObject}', but it also participates in an entity type hierarchy. Split mappings are not supported for hierarchies.

What it means

Thrown in the entity-splitting validator when an entity type has EntityTypeMappingFragment entries (split mappings) and also participates in an inheritance hierarchy — i.e. it has a BaseType or has directly derived types. Splitting (mapping one entity across multiple tables) is not supported for any type inside a hierarchy.

Solutions

Remove the split mapping (SplitToTable/fragments) from any type that is in a hierarchy.
Remove the inheritance relationship so the type is standalone before splitting it.
Move the columns into the main table instead of splitting when the type must stay in a hierarchy.

Example fix

// before
modelBuilder.Entity<Customer>().SplitToTable("CustomerExtras", t =>
    t.Property(c => c.Notes));
// SpecialCustomer : Customer -> throws 436

// after - do not split a type that is in a hierarchy
// either remove the split, or remove the inheritance
modelBuilder.Entity<Customer>().ToTable("Customers");
// put Notes in Customers, or split a non-hierarchical type

Defensive patterns

Strategy: validation

Validate before calling

foreach (var entityType in modelBuilder.Model.GetEntityTypes())
{
    var hasFragments = EntityTypeMappingFragment.Get(entityType) != null;
    if (!hasFragments) continue;
    if (entityType.BaseType != null || entityType.GetDirectlyDerivedTypes().Any())
        throw new InvalidOperationException($"{entityType.DisplayName()} uses split mapping but is in a hierarchy; splitting is unsupported for hierarchies.");
}

Prevention

Never combine SplitToTable with inheritance.
Before adding a base type to an entity, remove any SplitToTable configuration.
Add a model test asserting no split entity participates in a hierarchy.

When it happens

Trigger: Calling SplitToTable/EntityTypeMappingFragment configuration on an entity that has a base type or that other types derive from. The check is entityType.BaseType != null || entityType.GetDirectlyDerivedTypes().Any().

Common situations: Trying to split a base entity that is inherited from; combining table splitting with inheritance; refactor that introduced a base type after splitting was configured.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/24e92b3cf840fc42. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Relational/Infrastructure/RelationalModelValidator.cs:2378

    /// <summary>
    ///     Validates the mapping fragments for an entity type.
    /// </summary>
    /// <param name="entityType">The entity type to validate.</param>
    /// <param name="logger">The logger to use.</param>
    protected virtual void ValidateMappingFragment(
        IEntityType entityType,
        IDiagnosticsLogger<DbLoggerCategory.Model.Validation> logger)
    {
        var fragments = EntityTypeMappingFragment.Get(entityType);
        if (fragments == null)
        {
            return;
        }

        if (entityType.BaseType != null
            || entityType.GetDirectlyDerivedTypes().Any())
        {
            throw new InvalidOperationException(
                RelationalStrings.EntitySplittingHierarchy(entityType.DisplayName(), fragments.First().StoreObject.DisplayName()));
        }

        var anyTableFragments = false;
        var anyViewFragments = false;
        foreach (var fragment in fragments)
        {
            var mainStoreObject = StoreObjectIdentifier.Create(entityType, fragment.StoreObject.StoreObjectType);
            if (mainStoreObject == null)
            {
                throw new InvalidOperationException(
                    RelationalStrings.EntitySplittingUnmappedMainFragment(
                        entityType.DisplayName(), fragment.StoreObject.DisplayName(), fragment.StoreObject.StoreObjectType));
            }

            if (fragment.StoreObject == mainStoreObject)
            {
                throw new InvalidOperationException(

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