python - Django datetime primary key doesn't constrain unique -

so, here's model:

class mymodel(models.model):     timestamp = models.datetimefield(primary_key=true)     fielda = models.textfield() 

when call syncdb, django doesn't add constraint postgresql timestamp unique, though gives primary key constraint.

if change timestamp just unique=true, django creates unique constraint. however, if combine unique=true , primary_key=true, django doesn't create unique constraint.

my info:

• django-south v1.8
• django 1.4
• python 2.7
• postgresql 9.1

edit:

if save model same exact timestamp twice in 2 different runs (not same process), doesn't raise , integrityerror should. when creates unique constraint , no primary key, same code.

edit 2:

this code runs when have constraint "mymodel_pkey" primary key ("timestamp") in postgresql having timestamp = models.datetimefield(primary_key=true)

timestamp = datetime.datetime(2013, 7, 31, 0, 0, 0).replace(tzinfo=utc) print timestamp # prints 2013-07-31 00:00:00+00:00 row = mymodel(timestamp=timestamp, fielda='test') row.save() 

when run twice in row, doesn't raise integrityerror. however, unique=true , not primary_key=true, does raise integrityerror.

maybe example docs can bring light question

technically, primary key constraint combination of unique constraint , not-null constraint. so, following 2 table definitions accept same data:

create table products (   product_no integer unique not null,   name text,   price numeric );  create table products (   product_no integer primary key,   name text,   price numeric ); 

[...] primary key indicates column or group of columns can used unique identifier rows in table [...] adding primary key automatically create unique btree index on column or group of columns used in primary key. [...]