On Nov 27, 2013, at 1:23 AM, 史永宏 <shooting...@gmail.com> wrote:
> Hi, > Is there a solution for this issue today? Now I have a single table > Inheritance in table A, however, the type information is stored in another > table B linked from A with foreign key... > Now if I want to get polymorphic result when querying A, I got error ask me > to either use polymorphic or set enable_typechecks to False. > Any idea how to solve this? (After 3+ years)? this was solved two years ago, I failed to put a full migration doc for it but here’s the changelog: http://docs.sqlalchemy.org/en/rel_0_9/changelog/changelog_07.html#change-dc3aefb201de941ad86706e78e661813 [orm] [feature] polymorphic_on now accepts many new kinds of values: standalone expressions that aren’t otherwise mapped column_property() objects string names of any column_property() or attribute name of a mapped Column I just wrote an example for someone but as usual I can’t find it, so here it is again: from sqlalchemy import * from sqlalchemy.orm import * from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class AType(Base): __tablename__ = 'atype' id = Column(Integer, primary_key=True) name = Column(String) class A(Base): __tablename__ = 'a' id = Column(Integer, primary_key=True) data = Column(String) type_id = Column(ForeignKey('atype.id')) type_name = column_property(select([AType.name]).where(AType.id == id)) type = relationship(AType) __mapper_args__ = { "polymorphic_on": type_name, "polymorphic_identity": "a" } class ASub(A): __tablename__ = 'asub' id = Column(ForeignKey('a.id'), primary_key=True) __mapper_args__ = { "polymorphic_identity": "asub" } e = create_engine("sqlite://", echo=True) Base.metadata.create_all(e) sess = Session(e) a_type, asub_type = AType(name="a"), AType(name="asub") sess.add_all([ A(data='a1', type=a_type), ASub(data='asub1', type=asub_type), ASub(data='asub2', type=asub_type), A(data='a2', type=a_type), ]) sess.commit() sess = Session(e) for a in sess.query(A): print a.data, a.type > > On Thursday, May 20, 2010 12:22:34 PM UTC-7, Richard K wrote: > Hi Timmy and Michael, > > I was wandering here about the same problem. I have a table that defines keys > and value type (ie: key 'username', type 'unicode max 60' - that it is a > constant). > > Then, I have the values table, which is polymorphic on value type and also > has a fk to keys table. I think it is a bit lame to duplicate value type in > those two tables, and also not that useful to use the polymorphic as a > "static" value on each record of value table since I already have it on keys > table. By having a fk to keys table, can't I get the polymorphic value from > there? > > Thanks in advance, > Richard. > > On Wed, May 5, 2010 at 6:47 PM, Timmy Chan <timmy....@gmail.com> wrote: > thx, that is what i am wondering. they are one-to-one, maybe thats good > enough for performance. so there's no easy way to do this. > > > On Wed, May 5, 2010 at 5:44 PM, Michael Bayer <mik...@zzzcomputing.com> wrote: > > I meant SQL. if you want to do polymorphic_on based on "a.type" it would > at the very least need to issue: > > SELECT c.*, a.type JOIN b ON c.b_id = b.id JOIN a ON b.a_id=a > > which is an expensive way to get to where you're going. It can be done of > course but not through relation(). > > > On May 5, 2010, at 5:36 PM, Timmy Chan wrote: > >> "C"/"D" objects doesn't exist without "A" and "B"? maybe walk up the graph: >> C.b.a.type >> >> im not sure this schema is sensible, if it's really bad, please advise, im >> not attached to it! >> >> thax! >> >> On Wed, May 5, 2010 at 5:28 PM, Michael Bayer <mik...@zzzcomputing.com> >> wrote: >> what query do you want to see when you select "C" and "D" objects ? >> >> >> >> On May 5, 2010, at 5:26 PM, Timmy Chan wrote: >> >>> thx, is there a way to set that up, or something similar? >>> >>> after giving it thought, maybe polymorphic_on isn't what i need. in some >>> sense, table "A" is similar to a generic container, and i want to constrain >>> the type of "C" depending on "A"'s type column. is there a way to do this? >>> >>> On Wed, May 5, 2010 at 5:15 PM, Michael Bayer <mik...@zzzcomputing.com> >>> wrote: >>> >>> On May 5, 2010, at 5:01 PM, Timmy Chan wrote: >>> >>>> i have 4 tables, a, b, c, d. >>>> >>>> a has one-to-many relation with b, b with one-to-one relationship with c, >>>> c is a polymorphic on a.type, with d being one of the polymorphic types. >>>> >>>> is there a way to implement this? >>>> >>>> details: >>>> >>>> this is what im trying to do in sqlalchemy: >>>> >>>> a = Table('a', metadata, >>>> Column( 'id', Integer(), primary_key=True ), >>>> Column( 'type', UnicodeText() ) ) >>>> >>>> b = Table('b', metadata, >>>> Column( 'id', Integer(), primary_key=True ), >>>> Column( 'a_id', Integer(), ForeignKey('a.id') ) ) >>>> >>>> c = Table('c', metadata, >>>> Column( 'id', Integer(), primary_key=True ), >>>> Column( 'b_id', Integer(), ForeignKey('b.id') ), >>>> Column( 'class_id', Integer() ) ) >>>> >>>> d = Table('d', metadata, >>>> Column( 'id', Integer(), primary_key=True ), >>>> Column( 'data', Integer() ) >>>> >>>> mappers >>>> >>>> mapper( A, a ) >>>> mapper( B, b, properties={'a': relationship( A, >>>> uselist=False,backref='b', >>>> 'c':relationship( C, uselist=False, backref='b') }) >>>> >>>> # Does a full join, does not work >>>> mapper( C, c, polymorphic_on = a.c.type ) >>>> mapper( D, d, inherits=C, polymorphic_identity = "D" ) >>>> >>>> >>>> how can i change c to polymorphic on a, through the relationship? is >>>> there a way to sort by d.data? (b-c/d is one-on-one). >>> >>> this mapping is incorrect. mapper(C) cannot be polymorphic on a table >>> which is not part of its mapping, and mapper(C) does not contain an >>> "inherits" keyword to that of A. Usually the "polymorphic_on" setting is >>> on the base-most mapper in the hierarchy and its not clear here which >>> mapper you intend for that to be. >>> >>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To post to this group, send email to sqlal...@googlegroups.com. >>> To unsubscribe from this group, send email to >>> sqlalchemy+...@googlegroups.com. >>> For more options, visit this group at >>> http://groups.google.com/group/sqlalchemy?hl=en. >>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To post to this group, send email to sqlal...@googlegroups.com. >>> To unsubscribe from this group, send email to >>> sqlalchemy+...@googlegroups.com. >>> For more options, visit this group at >>> http://groups.google.com/group/sqlalchemy?hl=en. >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sqlalchemy" group. >> To post to this group, send email to sqlal...@googlegroups.com. >> To unsubscribe from this group, send email to >> sqlalchemy+...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/sqlalchemy?hl=en. >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sqlalchemy" group. >> To post to this group, send email to sqlal...@googlegroups.com. >> To unsubscribe from this group, send email to >> sqlalchemy+...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/sqlalchemy?hl=en. > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlal...@googlegroups.com. > To unsubscribe from this group, send email to sqlalchemy+...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlal...@googlegroups.com. > To unsubscribe from this group, send email to sqlalchemy+...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlal...@googlegroups.com. > To unsubscribe from this group, send email to sqlalchemy+...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > > -- > 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/groups/opt_out.
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