This is super! Thanks Michael On Wednesday, November 27, 2013 7:49:23 AM UTC-8, Michael Bayer wrote: > > > On Nov 27, 2013, at 1:23 AM, 史永宏 <shoot...@gmail.com <javascript:>> 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+...@googlegroups.com <javascript:>. > To post to this group, send email to sqlal...@googlegroups.com<javascript:> > . > 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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