Composite primary key support for write_lobs (CLOB/BLOB on CPK models)

[yahonda]

Background

PR #2693 added composite primary key (CPK) support across the adapter, but OracleEnhanced::DatabaseStatements#write_lobs (lib/active_record/connection_adapters/oracle_enhanced/database_statements.rb) still encodes a single-column primary-key assumption. A TODO comment was added there in the same PR; this issue tracks the actual fix.

Current code

def write_lobs(table_name, klass, attributes, columns) # :nodoc:
  id = quote(attributes[klass.primary_key])
  columns.each do |col|
    ...
    SELECT #{quote_column_name(col.name)} FROM #{quote_table_name(table_name)}
    WHERE #{quote_column_name(klass.primary_key)} = #{id} FOR UPDATE
    ...
  end
end

For a CPK model:

• klass.primary_key is an Array (e.g. ["author_id", "id"]).
• attributes[Array] returns nil.
• quote_column_name(Array) produces a malformed SQL fragment such as "[\"author_id\", \"id\"]".

Both the id lookup and the WHERE clause are wrong, so any CPK model that has a CLOB / BLOB column will fail in:

• insert_fixture (which calls write_lobs after super)
• The post-save LOB rewrite path used when prepared_statements: false (or for any LOB column that wasn't sent via the regular bind path)

Repro sketch

ActiveRecord::Schema.define do
  create_table :cpk_docs, primary_key: [:author_id, :id], force: true do |t|
    t.integer :author_id
    t.integer :id
    t.text    :body  # CLOB
  end
end

class CpkDoc < ActiveRecord::Base
  self.primary_key = [:author_id, :id]
end

CpkDoc.create!(id: [1, 1], body: "x" * 5000)
# => fails when write_lobs runs, because attributes[[:author_id, :id]] is nil
#    and the WHERE clause becomes WHERE "["author_id", "id"]" = ...

Fix sketch

Build the lookup key and the WHERE clause from the primary-key components:

def write_lobs(table_name, klass, attributes, columns) # :nodoc:
  pk_cols = Array(klass.primary_key)
  pk_pairs = pk_cols.map { |col| [col, attributes[col]] }
  where_clause = pk_pairs.map { |col, val| "#{quote_column_name(col)} = #{quote(val)}" }.join(" AND ")

  columns.each do |col|
    ...
    SELECT #{quote_column_name(col.name)} FROM #{quote_table_name(table_name)}
    WHERE #{where_clause} FOR UPDATE
    ...
  end
end

Specs should cover:

1. CPK + CLOB column, value above the varchar2 inline limit so the LOB rewrite path is exercised.
2. CPK + BLOB column.
3. The prepared_statements: false connection variant for the same scenarios.
4. insert_fixture against a CPK + LOB table (covers the insert_fixture call site).

Out of scope

• Composite-PK behaviour for non-LOB columns is already in Add composite primary key support #2693.
• Other call sites that still encode the single-column-PK assumption should be tracked in their own issues if discovered.

Related

• Add composite primary key support (track Rails 7.1+ feature) #2648 (umbrella CPK support)
• Add composite primary key support #2693 (the main CPK PR; added the TODO comment this issue tracks)