dotnet/efcore · error · InvalidOperationException

The type of the partition key property

Error message

The type of the partition key property '{property}' on '{entityType}' is '{propertyType}'. All partition key property types must be numeric, Boolean, or string, or converted to one of these types.

What it means

Thrown when a partition key property's effective store type is not string, numeric, or Boolean. Cosmos partition keys must be one of those primitive types (or a value converter to one of them). The validator unwrapping-nullable on the converter's ProviderClrType (or ClrType) and rejects anything else (e.g. Guid, DateTimeOffset, byte[]).

Solutions

Add a value converter that maps the property to string or a numeric type: .HasConversion<string>() (most common) or .HasConversion<long>().
Choose a different partition-key property that is already string/numeric/bool.
For enums, use HasConversion<int>() or HasConversion<string>().
For Guids, HasConversion<string>() is the typical fix.

Example fix

// before
modelBuilder.Entity<Event>().HasPartitionKey(e => e.EventId); // Guid

// after
modelBuilder.Entity<Event>()
    .Property(e => e.EventId).HasConversion<string>();
modelBuilder.Entity<Event>().HasPartitionKey(e => e.EventId);

Defensive patterns

Strategy: validation

Validate before calling

foreach (var et in dbContext.Model.GetEntityTypes())
{
    foreach (var name in et.GetPartitionKeyPropertyNames())
    {
        var p = et.FindProperty(name);
        if (p is null) continue;
        var t = (p.GetTypeMapping().Converter?.ProviderClrType ?? p.ClrType).UnwrapNullableType();
        if (t != typeof(string) && !t.IsNumeric() && t != typeof(bool))
            throw new InvalidOperationException($"{name} partition key type {t} not allowed");
    }
}

Prevention

Convert Guid/Date/enum partition key properties with HasConversion<string>() or HasConversion<int>().
Prefer string or long for partition keys.
Add a model-validation unit test asserting partition key store types.

When it happens

Trigger: Configuring HasPartitionKey on a property whose ClrType is Guid, DateTime, DateTimeOffset, byte[], enum (without conversion), or any custom struct, without a value converter to a numeric/string/bool type. Fires during ValidateKeys.

Common situations: Partitioning by a Guid id directly; partitioning by a DateTime column; using an enum as the partition key without a numeric/string converter; new partition key on a property whose type was chosen for business logic, not Cosmos compatibility.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/e65f3aafab352e1a. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Infrastructure/Internal/CosmosModelValidator.cs:477

                    CosmosStrings.PartitionKeyNotOnRoot(entityType.DisplayName(), entityType.BaseType.DisplayName()));
            }

            foreach (var partitionKeyPropertyName in partitionKeyPropertyNames)
            {
                var partitionKey = entityType.FindProperty(partitionKeyPropertyName);
                if (partitionKey == null)
                {
                    throw new InvalidOperationException(
                        CosmosStrings.PartitionKeyMissingProperty(entityType.DisplayName(), partitionKeyPropertyName));
                }

                var partitionKeyType = (partitionKey.GetTypeMapping().Converter?.ProviderClrType
                    ?? partitionKey.ClrType).UnwrapNullableType();
                if (partitionKeyType != typeof(string)
                    && !partitionKeyType.IsNumeric()
                    && partitionKeyType != typeof(bool))
                {
                    throw new InvalidOperationException(
                        CosmosStrings.PartitionKeyBadStoreType(
                            partitionKeyPropertyName,
                            entityType.DisplayName(),
                            partitionKeyType.ShortDisplayName()));
                }
            }
        }
    }

    /// <summary>
    ///     Validates that a key doesn't have mutable properties.
    /// </summary>
    /// <param name="key">The key to validate.</param>
    /// <param name="logger">The logger to use.</param>
    protected override void ValidateMutableKey(
        IKey key,
        IDiagnosticsLogger<DbLoggerCategory.Model.Validation> logger)
    {

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