upsert_all / insert_all! (mutation path) corrupt non-integer composite primary key columns by casting them with BigInteger #407

Environment details

• Programming language: Ruby
• OS: Linux (also reproduced on Spanner emulator and a real Spanner database)
• Language runtime version: Ruby 3.4.8
• Package version: activerecord-spanner-adapter 2.5.0 (also present on main — see _set_composite_primary_key_value)
• Rails: 8.0.4
• Spanner dialect: GoogleSQL

Steps to reproduce

1. Create a table with a composite primary key that includes STRING columns (minimal fictional schema below).
2. Outside a DML transaction (default mutation / InsertOrUpdate path), call Model.upsert_all([row]) or Model.insert_all!([row]) with a hash of plain Ruby values.
3. Read the row back and inspect the primary key columns.

create_table :demo_items, id: false, force: true do |t|
  t.integer  :account_id, null: false
  t.string   :resource_uuid, null: false   # UUID string
  t.string   :kind, null: false            # e.g. "email"
  t.string   :value, null: false           # e.g. "alice@example.com"
  t.string   :resource_type, null: false   # non-PK column
  t.datetime :created_at, null: false
end

execute <<~SQL
  ALTER TABLE demo_items
  ADD PRIMARY KEY (account_id, resource_uuid, kind, value)
SQL

class DemoItem < ActiveRecord::Base
  self.table_name = "demo_items"
  self.primary_key = %w[account_id resource_uuid kind value]
end

account_id = 4242
resource_uuid = "89ff73aa-c1cb-475e-bb27-89281c50c5b8"
created_at = Time.utc(2026, 1, 1, 12, 0, 0)

DemoItem.where(account_id: account_id).delete_all

row = {
  "account_id" => account_id,
  "resource_uuid" => resource_uuid,
  "kind" => "email",
  "value" => "alice@example.com",
  "resource_type" => "house",
  "created_at" => created_at,
}

# Mutation path (default when outside a DML transaction)
DemoItem.upsert_all([row])
# DemoItem.insert_all!([row])  # same corruption on the mutation path

puts DemoItem.where(account_id: account_id).map(&:attributes)

Actual result

[{
  "account_id" => 4242,
  "resource_uuid" => "89",          # truncated via BigInteger.cast
  "kind" => "0",                    # "email" => 0
  "value" => "0",                   # "alice@example.com" => 0
  "resource_type" => "house",       # non-PK: OK
  "created_at" => 2026-01-01 12:00:00 UTC, # non-PK: OK
}]

Lookup by the intended PK returns nil:

DemoItem.find_by(
  account_id: account_id,
  resource_uuid: resource_uuid,
  kind: "email",
  value: "alice@example.com"
)
# => nil

Expected result

Row persisted with the original STRING PK values (resource_uuid, kind, value unchanged).

Root cause

In lib/activerecord_spanner_adapter/base.rb, _set_composite_primary_key_value always defaults the type to BigInteger unless the caller already wrapped the value in ActiveModel::Attribute:

def self._set_composite_primary_key_value primary_key, values, is_mutation
  value = values[primary_key]
  type = ActiveModel::Type::BigInteger.new  # <-- always, for every composite PK column

  if value.is_a? ActiveModel::Attribute
    type = value.type
    value = value.value
  end
  # ...
  values[primary_key] =
    ActiveModel::Attribute.from_database primary_key, value, type
end

Cast examples:

This path is used by _buffer_record for mutation writes (insert / insert_or_update), which is what upsert_all and insert_all! use by default when there is no open DML transaction (or when isolation is :buffered_mutations).

Inside a default ActiveRecord DML transaction, the same call goes through SQL DML and does not hit this cast — so the bug is mutation-path-specific.

insert_all (without bang) uses DML INSERT OR IGNORE and is not affected; under :buffered_mutations the adapter raises NotImplementedError for that method.

Suggested fix

When rewriting composite PK values, use the column's actual ActiveRecord type (e.g. type_for_attribute(primary_key) / columns_hash[primary_key].type) instead of hard-coding ActiveModel::Type::BigInteger, at least when a non-nil client-provided value is present.

Integer / auto-generated PK columns would keep working; STRING (and other non-INT64) composite PK columns would stop being corrupted.

Workaround (application-side)

Wrap each composite PK column with the real column type before upsert_all / insert_all! on the mutation path only:

row = {
  "account_id" => 4242,
  "resource_uuid" => "89ff73aa-c1cb-475e-bb27-89281c50c5b8",
  "kind" => "email",
  "value" => "alice@example.com",
  "resource_type" => "house",
  "created_at" => Time.utc(2026, 1, 1, 12, 0, 0),
}

Array(DemoItem.primary_key).each do |column|
  row[column] = ActiveModel::Attribute.from_database(
    column,
    row[column],
    DemoItem.type_for_attribute(column)
  )
end

DemoItem.upsert_all([row])
# => persists correct PK values on the mutation path

Important: do not apply this wrapping inside a DML transaction. In that path, ActiveModel::Attribute wrappers can be persisted as NULL. Only type PK columns when there is no open DML transaction (or when isolation is :buffered_mutations).

stringify_keys alone does not fix it; only pre-wrapping with the correct ActiveModel::Attribute type does.

Notes

• Reproduced on Spanner emulator and on a real Spanner instance (so this is not an emulator-only quirk).
• Happy to contribute a failing test + patch if that would help.