Add foreign_keys accessor to SQLite Database objects, which modifies …

…the foreign_keys PRAGMA available in 3.6.19+

I hadn't noticed this before, but all PRAGMA modification operations
in the shared SQLite adapter are not thread safe.  The only reason
this wasn't caught before is because it's likely few people use them
and few people run SQLite in a threaded environment, and the
intersection of those groups is probably very small.

A future commit will address this by making all PRAGMA modification
operators apply directly on the underlying connection objects
inside Database#connect, by specifying the options as database
options when calling Sequel.connect.  That's the only thread-safe
simple way to do it.

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* Add foreign_keys accessor to SQLite Database objects, which modifies the foreign_keys PRAGMA available in 3.6.19+ (jeremyevans)
+
 * Add an Database#sqlite_version method when connecting to SQLite, used to determine feature support (jeremyevans)
 
 * Fix rolling back transactions when connecting to Oracle via JDBC (jeremyevans)

lib/sequel/adapters/shared/sqlite.rb

@@ -31,6 +31,18 @@ def auto_vacuum=(value)
       def database_type
         :sqlite
       end
+
+      # Boolean signifying the value of the foreign_keys PRAGMA, or nil
+      # if not using SQLite 3.6.19+.
+      def foreign_keys
+        pragma_get(:foreign_keys).to_i == 1 if sqlite_version >= 30619
+      end
+
+      # Set the foreign_keys PRAGMA using the given boolean value, if using
+      # SQLite 3.6.19+.  If not using 3.6.19+, no error is raised.
+      def foreign_keys=(value)
+        pragma_set(:foreign_keys, !!value ? 'on' : 'off') if sqlite_version >= 30619
+      end
 
       # Return a hash containing index information. Hash keys are index name symbols.
       # Values are subhashes with two keys, :columns and :unique.  The value of :columns

spec/adapters/sqlite_spec.rb

@@ -36,6 +36,34 @@
     end
   end
 
+  specify "should provide the SQLite version as an integer" do
+    @db.sqlite_version.should be_a_kind_of(Integer)
+  end
+
+  specify "should support setting and getting the foreign_keys pragma" do
+    (@db.sqlite_version >= 30619 ? [true, false] : [nil]).should include(@db.foreign_keys)
+    @db.foreign_keys = true
+    @db.foreign_keys = false
+  end
+
+  if SQLITE_DB.sqlite_version >= 30619
+    specify "should enforce foreign key integrity if foreign_keys pragma is set" do
+      @db.foreign_keys = true
+      @db.create_table!(:fk){primary_key :id; foreign_key :parent_id, :fk}
+      @db[:fk].insert(1, nil)
+      @db[:fk].insert(2, 1)
+      @db[:fk].insert(3, 3)
+      proc{@db[:fk].insert(4, 5)}.should raise_error(Sequel::Error)
+    end
+  end
+
+  specify "should not enforce foreign key integrity if foreign_keys pragma is unset" do
+    @db.foreign_keys = false
+    @db.create_table!(:fk){primary_key :id; foreign_key :parent_id, :fk}
+    @db[:fk].insert(1, 2)
+    @db[:fk].all.should == [{:id=>1, :parent_id=>2}]
+  end
+
   specify "should provide a list of existing tables" do
     @db.drop_table(:testing) rescue nil
     @db.tables.should be_a_kind_of(Array)