Changes between Version 3 and Version 4 of FGDBSpecification

Timestamp:

Oct 8, 2013, 4:18:31 PM (11 years ago)

Author:

Even Rouault

Comment:

Fix null fields flag

FGDBSpecification

@@ -65 +65 @@
 ||'''Format'''||'''Content'''||
 || int32 || maximum length of string ||
-|| ubyte || unknown role ||
+|| ubyte || flag ||
 || ubyte || unknown role ||
 
@@ -114 +114 @@
 ||'''Format'''||'''Content'''||
 || ubyte || width : 38 ||
-|| ubyte || unknown role ||
+|| ubyte || flag ||
 
 
@@ -121 +121 @@
 ||'''Format'''||'''Content'''||
 || ubyte || width in bytes (e.g. 2 for int16, 4 for int32, 4 for float32, 8 for float64, 8 for datetime) ||
-|| ubyte || unknown role ||
-|| ubyte || unknown role ||
+|| ubyte || flag ||
+|| ubyte || unknown role ||
+
+If the lsb of the flag field (when present) is set to 1, then the field can be null.
+
+FIXME: find which byte is the flag field for geometry fields. They are supposed to be nullable for now.
+
 
 == Rows section ==
@@ -138 +143 @@
 ||'''Format'''||'''Content'''||
 || int32 || length in bytes of the row blob ( this field excluded) ||
-|| ceil(number_fields / 8) * ubyte || flags describing if a field is null. See below explanation ||
+|| ceil(number_nullable_fields / 8) * ubyte || flags describing if a field is null. See below explanation ||
 
 === Null fields flags ===
 
-Each bit of the flags field encode for the presence or absence of the field content for the row.
+Each bit of the flags field encode for the presence or absence of the field content, for a nullable field, for the row.
 The flag is set to 1 if the field is missing/null, or 0 if the field is present/non-null (0 is used as well for spare bytes).
 The flag for the first field, in the order of the fields of the field description section (typically the geometry),
 is the least significant bit of the first byte of the flags field.
 
-Note: there's no explicit data for OBJECTID and no flag bit for it. It must be ignored when considering
-the list of fields (for number_fields value in particular).
+There are no bits reserved for non-nullable fields.
+
+If all fields are non-nullable, the flag field is absent.
+
+Note: there's no explicit data for OBJECTID and no reserved flag bit for it.
 
 For each non-null field, the field content is appended in the order of the fields of the field