dotnet/efcore · error · InvalidOperationException

The entity type ' ' is sharing the container ' ' with other…

Error message

The entity type '{entityType}' is sharing the container '{container}' with other types, but does not have a discriminator value configured. Configure a unique discriminator value for this entity type.

What it means

CosmosModelValidator.ValidateSharedContainerCompatibility throws InvalidOperationException(CosmosStrings.NoDiscriminatorValue) when an instantiable entity type sharing a container has a discriminator property configured but no discriminator value assigned (entityType.GetDiscriminatorValue() == null). EF needs a concrete value to write into the discriminator field for each document so it can route queries to the correct type.

Solutions

1. Add HasValue(...) right after HasDiscriminator for every instantiable type sharing the container.
2. If using attributes, make sure each type carries a [Discriminator] value (or whatever attribute the configuration reads).
3. If the type is meant to be abstract, ensure ClrType is abstract so IsInstantiable() returns false and skips this check.
4. Run model validation at startup to surface missing values before the first SaveChanges.

Example fix

// before - throws: discriminator property set, no value
modelBuilder.Entity<A>()
    .ToContainer("Shared")
    .HasDiscriminator(a => a.Kind);

// after - assign a value
modelBuilder.Entity<A>()
    .ToContainer("Shared")
    .HasDiscriminator(a => a.Kind).HasValue("a");

// Pre-validate: every instantiable shared-container type with a discriminator must also have a value.
static bool AllHaveDiscriminatorValues(IReadOnlyList<IEntityType> types)
    => types.Where(t => t.ClrType.IsInstantiable() && t.GetContainingPropertyName() is null)
        .All(t => t.GetDiscriminatorValue() is not null);

When it happens

Trigger: Calling HasDiscriminator(x => x.Kind) without a following HasValue(...); configuring a discriminator property via attribute or convention but never setting the value; abstract base types where the default convention would skip the value but the type became instantiable.

Common situations: Forgetting HasValue after HasDiscriminator; switching from default-discriminator conventions to explicit configuration and missing the value; discriminator value lost during a refactor.

Related errors

• The discriminator value for
• The entity type ' ' is sharing the container ' ' with other…
• The partition key properties for entity type
• The partition key property
• An Azure Cosmos DB container name is defined on entity type

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/9c65571506323535. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Infrastructure/Internal/CosmosModelValidator.cs:207

            }

            if (mappedTypes.Count == 1)
            {
                break;
            }

            if (entityType.ClrType.IsInstantiable()
                && entityType.GetContainingPropertyName() == null)
            {
                if (entityType.FindDiscriminatorProperty() == null)
                {
                    throw new InvalidOperationException(CosmosStrings.NoDiscriminatorProperty(entityType.DisplayName(), container));
                }

                var discriminatorValue = entityType.GetDiscriminatorValue();
                if (discriminatorValue == null)
                {
                    throw new InvalidOperationException(CosmosStrings.NoDiscriminatorValue(entityType.DisplayName(), container));
                }

                if (discriminatorValues.TryGetValue(discriminatorValue, out var duplicateEntityType))
                {
                    throw new InvalidOperationException(
                        CosmosStrings.DuplicateDiscriminatorValue(
                            entityType.DisplayName(),
                            discriminatorValue,
                            duplicateEntityType.DisplayName(),
                            container));
                }

                discriminatorValues[discriminatorValue] = entityType;

                var currentIsDiscriminatorMappingComplete = entityType.GetIsDiscriminatorMappingComplete();
                if (isDiscriminatorMappingComplete == null)
                {
                    isDiscriminatorMappingComplete = currentIsDiscriminatorMappingComplete;

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