Hi Mike, thanks a lot for your help.
I know the concepts of db-normalization and 3NF - but haven't worked so much with that in practice. One of my problems is that I think the object-orientated way. I started quite early to work with OODBMS instead of RDBMS. I an OODBMS SetSet would just a list/array inside of TrainingUnit. I wouldn't need to take care about relation tables or object ids - the OODBMS make this for me. But at this project I have no choice - I need an RDBMS. On 2015-09-29 12:04 Mike Bayer <mike...@zzzcomputing.com> wrote: > > sqlite> SELECT a_oid, b_oid FROM a_b_relation; > > 1|1 > > 1|1 > > > > You see here that `a` has two references to the same entity/row `b`. > > In my data structure this make sense. But maybe it break a > > SQL-/RDBMS-rule? > it does, it breaks first normal form in that there is no primary key > (http://www.tutorialspoint.com/sql/first-normal-form.htm). But does a relation-table need a primary key? For me a relational-table is just a helper-table (or a workaround) because RDBMS doesn't support "native" 1-to-n or m-to-n references. The normal-form-rules does have to fit to all(!) tables including relation-tables? > OK but those are not the same SetSet, they happened at two different > times. They should be separate entities of data. I understand what you mean. But the data in SetSet haven't a time-dimension. The time (as a date) is coded in the TrainingUnit. There is a attribute/row fort that. > would like SetSet objects to be unique on their reps/weight, then the > association table itself would become an entity in which case you'd > need to add an additional column to it as a primary key. I am not really getting into that. Everytime i try to rearange my current structure I ran into the same problem. This is the real (little bit snipped) structure, where I can not see how this would help me, when I add a primary-key to the table named 'tu_set_relation'. tu_set_relation = sa.Table('tu_set_relation', _Base.metadata, sa.Column('tu_oid', sa.Integer, sa.ForeignKey('TrainingUnit.oid')), sa.Column('set_oid', sa.Integer, sa.ForeignKey('SetSet.oid')) ) class TrainingUnit(_Base): __tablename__ = 'TrainingUnit' _oid = sa.Column('oid', sa.Integer, primary_key=True) _date = sa.Column('date', sa.Date) _sets = sao.relationship('SetSet', secondary=tu_set_relation), _machine_fk = sa.Column('machine', sa.Integer, sa.ForeignKey('Machine.oid')) _machine = sao.relationship("Machine") class SetSet(_Base): __tablename__ = 'SetSet' # 'Set' is a reserved word in SQL _oid = sa.Column('oid', sa.Integer, primary_key=True) _repetitions = sa.Column('repetitions', sa.Integer) _level = sa.Column('level', sa.Integer) -- -----BEGIN PGP PUBLIC KEY BLOCK----- Version: GnuPG v1 mQENBFQIluABCACfPwAhRAwFD3NXgv5CtVUGSiqdfJGVViVBqaKd+14E0pASA0MU G0Ewj7O7cGy/ZIoiZ0+lIEZmzJKHfuGwYhXjR/PhnUDrQIHLBvh9WuD6JQuULXfH kXtVm/i9wm76QAcvr2pwYgNzhcJntUHl2GcgnInYbZDeVmg+p9yIPJjuq73/lRS3 0/McgNoFOBhKK/S6STQuFyjr9OyJyYd1shoM3hmy+kg0HYm6OgQBJNg92WV9jwGe GzlipvEp2jpLwVsTxYir2oOPhfd9D1fC9F/l/3gXbfjd5GIIVrZFq2haZmoVeJ33 LJxo3RA5Tf9LoUeels1b4s9kFz6h7+AHERUpABEBAAG0IUNocmlzdGlhbiBCdWh0 eiA8YnVodHpAcG9zdGVvLmRlPokBPgQTAQIAKAUCVAiW4AIbAwUJAeEzgAYLCQgH AwIGFQgCCQoLBBYCAwECHgECF4AACgkQZLsXsAdRqOxNUAf/V/hDA5zGDpySuCEj DhjiVRK74J9Wd8gfH0WAf1Co5HZ24wZH8rgOIVIgXw8rWkOw/VA6xfdfT+64xjTY Fhkpbrk199nDzp72F7Jc4NC+x8xac2e3rK5ifSWhZx7L5A32pGYE+d16m3EEqImK D4gcZl38x9zdUnD4hHyXkIPz1uCfuMuGgWEnaUk4Wbj41CBZr3O0ABue6regV15U jaes8r+B8iCcY+0yP2kse+3iaCaMqNv5FgQZ9+b2Cql8pFkZJVtBVUw4GW3DWZJi du0O/YrC9TgS+xY9ht/MD2qSHwjcK1sdImjqBO7xP8TIOwKeYyDvGKnSO3EJ/sSA UPGEPrkBDQRUCJbgAQgA0k/Qg67CCUJE2/zuxBEoK4wLJpDRJzh8CQPZpjWx8VP0 KL892jwfxymXn8KNhuy1SgCBFSeV9jg4VZNWDlUGJc2lo82ajr9PzIsrQwu4lf0B zrUWV5hWepKu/kb8uSjx58YYfx0SFz4+9akX3Wwu9TUHntzL5Gk3Q26nnsr1xEJ+ VEumvCH9AE0Tk0K7dQpJ2/JcLuO+uhrpd/lHFDYVN5NsG3P015uFOkDI6N/xNFCj v95XNR93QlfKpK3qWlFGescfG+o/7Ub6s67/i/JoNbw0XgPEHmQfXpD7IHO4cu+p +ETb11cz+1mmi96cy98ID+uTiToJ8G//yD9rmtyxoQARAQABiQElBBgBAgAPBQJU CJbgAhsMBQkB4TOAAAoJEGS7F7AHUajs6sQH/iKs6sPc0vkRJLfbwrijZeecwCWF blo/jzIQ8jPykAj9SLjV20Xwqg3XcJyko8ZU6/zuRJq9xjlv9pZr/oVudQAt6v+h 2Cf4rKEjmau483wjMV2xjTXQhZi9+ttDbia4fgdmGtKsOicn5ae2fFXcXNPu3RiW sZKifWdokA6xqMW6iIG9YjjI5ShxngHWp2xfPscBFMDRtFOMags/Yx+YvwoyEZ4A dURYMFHFqpwILEc8hIzhRg1gq40AHbOaEdczS1Rr3T7/gS6eBs4u6HuY5g2Bierm lLjpspFPjMXwJAa/XLOBjMF2vsHPrZNcouNKkumQ36yq/Pm6DFXAseQDxOk= =PGP9 -----END PGP PUBLIC KEY BLOCK----- -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
