added _id handling; the _id field must always be the first field in

a bson document. Handling it at this "low" level makes things easier
in the layers above

bson/constants/constants.factor

@@ -11,6 +11,8 @@ TUPLE: oid { a initial: 0 } { b initial: 0 } ;
 
 TUPLE: objref ns objid ;
 
+CONSTANT: MDB_OID_FIELD "_id"
+
 CONSTANT: T_EOO  0  
 CONSTANT: T_Double  1  
 CONSTANT: T_Integer  16  

bson/writer/writer.factor

@@ -93,9 +93,16 @@ M: sequence bson-write ( array -- )
         [ length 5 + bson-write ] keep
         write
         write-eoo ; 
-    
+
+: write-oid ( hashtable -- )
+    [ MDB_OID_FIELD ] dip at*
+    [ [ MDB_OID_FIELD ] dip write-pair ] [ drop ] if ; inline
+
+: oid-field? ( name -- boolean )
+    MDB_OID_FIELD = ; inline
+
 M: assoc bson-write ( hashtable -- )
-    '[ _ [ write-pair ] assoc-each ]
+    '[ _ [ write-oid ] [ [ over oid-field? [ 2drop ] [ write-pair ] if ] assoc-each ] bi ]
     binary swap with-byte-writer
     [ length 5 + bson-write ] keep
     write

mongodb/operations/operations.factor

@@ -120,7 +120,7 @@ M: mdb-reply-op (read-message) ( msg-stub opcode -- message )
     read-longlong >>cursor
     read-int32 >>start#
     read-int32 [ >>returned# ] keep
-    [ <linked-hash> stream>assoc drop ] accumulator [ times ] dip >>objects ;    
+    [ H{ } stream>assoc drop ] accumulator [ times ] dip >>objects ;    
 
 : read-header ( message -- message )
     read-int32 >>length
@@ -151,7 +151,7 @@ PRIVATE>
      write flush ; inline
 
 : build-query-object ( query -- selector )
-    [let | selector [ <linked-hash> ] |
+    [let | selector [ H{ } clone ] |
         { [ orderby>> [ "orderby" selector set-at ] when* ]
           [ explain>> [ "$explain" selector set-at ] when* ]
           [ hint>> [ "$hint" selector set-at ] when* ]