Added Hamming distance for MySQL

README.md

@@ -417,9 +417,28 @@ Supported values are:
 
 - `euclidean`
 - `cosine`
+- `hamming`
 
 Note: The `DISTANCE()` function is [only available on HeatWave](https://dev.mysql.com/doc/refman/9.0/en/vector-functions.html)
 
+### Binary Vectors
+
+Use the `binary` type to store binary vectors
+
+```ruby
+class AddEmbeddingToItems < ActiveRecord::Migration[7.2]
+  def change
+    add_column :items, :embedding, :binary
+  end
+end
+```
+
+Get the nearest neighbors by Hamming distance
+
+```ruby
+Item.nearest_neighbors(:embedding, "\x05", distance: "hamming").first(5)
+```
+
 ## Examples
 
 - [Embeddings](#openai-embeddings) with OpenAI

lib/neighbor/model.rb

@@ -66,6 +66,7 @@ def self.neighbor_attributes
             dimensions = v[:dimensions]
             dimensions ||= column_info&.limit unless column_info&.type == :binary
             type = v[:type] || column_info&.type
+            type = :bit if type == :binary && adapter == :mysql
 
             if !Neighbor::Utils.validate_dimensions(value, type, dimensions, adapter).nil?
               errors.add(k, "must have #{dimensions} dimensions")
@@ -144,7 +145,11 @@ def self.neighbor_attributes
             when :mariadb
               "VEC_DISTANCE(#{quoted_attribute}, #{query})"
             when :mysql
-              "DISTANCE(#{quoted_attribute}, #{query}, #{connection.quote(operator)})"
+              if operator == "BIT_COUNT"
+                "BIT_COUNT(#{quoted_attribute} ^ #{query})"
+              else
+                "DISTANCE(#{quoted_attribute}, #{query}, #{connection.quote(operator)})"
+              end
             else
               if operator == "#"
                 "bit_count(#{quoted_attribute} # #{query})"

lib/neighbor/utils.rb

@@ -2,7 +2,7 @@ module Neighbor
   module Utils
     def self.validate_dimensions(value, type, expected, adapter)
       dimensions = type == :sparsevec ? value.dimensions : value.size
-      dimensions *= 8 if type == :bit && adapter == :sqlite
+      dimensions *= 8 if type == :bit && [:sqlite, :mysql].include?(adapter)
       if expected && dimensions != expected
         "Expected #{expected} dimensions, not #{dimensions}"
       end
@@ -20,6 +20,8 @@ def self.validate_finite(value, type)
     end
 
     def self.validate(value, dimensions:, type:, adapter:)
+      type = :bit if type == :binary && adapter == :mysql
+
       if (message = validate_dimensions(value, type, dimensions, adapter))
         raise Error, message
       end
@@ -87,6 +89,11 @@ def self.operator(adapter, column_type, distance)
           when "euclidean"
             "EUCLIDEAN"
           end
+        when :binary
+          case distance
+          when "hamming"
+            "BIT_COUNT"
+          end
         else
           raise ArgumentError, "Unsupported type: #{column_type}"
         end

test/mysql_bit_test.rb

@@ -0,0 +1,35 @@
+require_relative "test_helper"
+require_relative "support/mysql"
+
+class MysqlBitTest < Minitest::Test
+  def setup
+    MysqlItem.delete_all
+  end
+
+  def test_hamming
+    create_bit_items
+    result = MysqlItem.find(1).nearest_neighbors(:binary_embedding, distance: "hamming").first(3)
+    assert_equal [2, 3], result.map(&:id)
+    assert_elements_in_delta [2, 3].map { |v| v * 1024 }, result.map(&:neighbor_distance)
+  end
+
+  def test_hamming_scope
+    create_bit_items
+    result = MysqlItem.nearest_neighbors(:binary_embedding, "\x05" * 1024, distance: "hamming").first(5)
+    assert_equal [2, 3, 1], result.map(&:id)
+    assert_elements_in_delta [0, 1, 2].map { |v| v * 1024 }, result.map(&:neighbor_distance)
+  end
+
+  def test_invalid_dimensions
+    error = assert_raises(ActiveRecord::RecordInvalid) do
+      MysqlItem.create!(binary_embedding: "\x00" * 1024 + "\x11")
+    end
+    assert_equal "Validation failed: Binary embedding must have 8192 dimensions", error.message
+  end
+
+  def create_bit_items
+    MysqlItem.create!(id: 1, binary_embedding: "\x00" * 1024)
+    MysqlItem.create!(id: 2, binary_embedding: "\x05" * 1024)
+    MysqlItem.create!(id: 3, binary_embedding: "\x07" * 1024)
+  end
+end

test/support/mysql.rb

@@ -12,11 +12,13 @@ class MysqlRecord < ActiveRecord::Base
 MysqlRecord.connection.instance_eval do
   create_table :mysql_items, force: true do |t|
     t.vector :embedding, limit: 3
+    t.binary :binary_embedding
   end
 end
 
 class MysqlItem < MysqlRecord
   has_neighbors :embedding
+  has_neighbors :binary_embedding, dimensions: 8192
 end
 
 # ensure has_neighbors does not cause model schema to load