Support boolean source '$exists foo.bar.baz'

The seemingly unrelated test change is to prevent an exception in
BSON.serialize.

Gemfile.lock

@@ -2,6 +2,7 @@ PATH
   remote: .
   specs:
     mosql (0.4.0)
+      bson (~> 1.10.2)
       bson_ext
       json
       log4r

lib/mosql/schema.rb

@@ -159,10 +159,24 @@ def fetch_and_delete_dotted(obj, dotted)
       val
     end
 
-    def fetch_special_source(obj, source)
+    def fetch_exists(obj, dotted)
+      pieces = dotted.split(".")
+      while pieces.length > 1
+        key = pieces.shift
+        obj = obj[key]
+        return false unless obj.is_a?(Hash)
+      end
+      obj.has_key?(pieces.first)
+    end
+
+    def fetch_special_source(obj, source, original)
       case source
       when "$timestamp"
         Sequel.function(:now)
+      when /^\$exists (.+)/
+        # We need to look in the cloned original object, not in the version that
+        # has had some fields deleted.
+        fetch_exists(original, $1)
       else
         raise SchemaError.new("Unknown source: #{source}")
       end
@@ -189,14 +203,15 @@ def transform(ns, obj, schema=nil)
       schema ||= find_ns!(ns)
 
       obj = obj.dup
+      original = BSON.deserialize(BSON.serialize(obj))
       row = []
       schema[:columns].each do |col|
 
         source = col[:source]
         type = col[:type]
 
         if source.start_with?("$")
-          v = fetch_special_source(obj, source)
+          v = fetch_special_source(obj, source, original)
         else
           v = fetch_and_delete_dotted(obj, source)
           case v

mosql.gemspec

@@ -19,6 +19,7 @@ Gem::Specification.new do |gem|
   %w[sequel pg mongo bson_ext rake log4r json
      ].each { |dep| gem.add_runtime_dependency(dep) }
   gem.add_runtime_dependency "mongoriver", "0.4"
+  gem.add_runtime_dependency "bson", "~> 1.10.2"
 
   gem.add_development_dependency "minitest"
   gem.add_development_dependency "mocha"

test/functional/streamer.rb

@@ -262,7 +262,7 @@ def build_streamer
             @streamer.handle_op({ 'ns' => 'mosql_test.collection',
                                   'op' => 'u',
                                   'o2' => { '_id' => 'a' },
-                                  'o'  => { 'var' => 1 << 70 },
+                                  'o'  => { 'var' => 1 << 62 },
                                 })
           end
         end
@@ -272,7 +272,7 @@ def build_streamer
           @streamer.handle_op({ 'ns' => 'mosql_test.collection',
                                 'op' => 'u',
                                 'o2' => { '_id' => 'a' },
-                                'o'  => { 'var' => 1 << 70 },
+                                'o'  => { 'var' => 1 << 62 },
                               })
           assert_equal(0, sequel[:sqltable].where(:_id => 'a').count)
         end

test/unit/lib/mosql/schema.rb

@@ -343,6 +343,26 @@ def check(orig, path, expect, result)
       - mosql_created:
         :source: $timestamp
         :type: timestamp
+  existence:
+    :meta:
+      :table: b_table
+    :columns:
+      - _id: TEXT
+      - has_foo:
+        :source: $exists foo
+        :type: BOOLEAN
+      - has_foo_bar:
+        :source: $exists foo.bar
+        :type: BOOLEAN
+  exists_and_value:
+    :meta:
+      :table: c_table
+    :columns:
+      - _id: TEXT
+      - foo: TEXT
+      - has_foo:
+        :source: $exists foo
+        :type: BOOLEAN
   invalid:
     :meta:
       :table: invalid
@@ -362,6 +382,28 @@ def check(orig, path, expect, result)
       assert_equal(['a', Sequel.function(:now)], r)
     end
 
+    it 'translates $exists' do
+      r = @othermap.transform('db.existence', { '_id' => 'a' })
+      assert_equal(['a', false, false], r)
+      r = @othermap.transform('db.existence', { '_id' => 'a', 'foo' => nil })
+      assert_equal(['a', true, false], r)
+      r = @othermap.transform('db.existence', { '_id' => 'a', 'foo' => {} })
+      assert_equal(['a', true, false], r)
+      r = @othermap.transform('db.existence', { '_id' => 'a', 'foo' => {'bar' => nil} })
+      assert_equal(['a', true, true], r)
+      r = @othermap.transform('db.existence', { '_id' => 'a', 'foo' => {'bar' => 42} })
+      assert_equal(['a', true, true], r)
+    end
+
+    it 'can get $exists and value' do
+      r = @othermap.transform('db.exists_and_value', { '_id' => 'a' })
+      assert_equal(['a', nil, false], r)
+      r = @othermap.transform('db.exists_and_value', { '_id' => 'a', 'foo' => nil })
+      assert_equal(['a', nil, true], r)
+      r = @othermap.transform('db.exists_and_value', { '_id' => 'a', 'foo' => 'xxx' })
+      assert_equal(['a', 'xxx', true], r)
+    end
+
     it 'rejects unknown specials' do
       assert_raises(MoSQL::SchemaError) do
         r = @othermap.transform('db.invalid', { '_id' => 'a' })