Oh right, I've used the @property decorator before, just been a while. Thanks for the explanation of @hybrid_property. Makes sense.
On Wed, Jun 7, 2017 at 5:32 PM, mike bayer <mike...@zzzcomputing.com> wrote: > > > On 06/07/2017 06:19 PM, Greg Silverman wrote: > >> Thanks, it worked! >> >> I tried something similar using the @hybrid_property decorator, but could >> not get it to work. What exactly is the difference between that and the >> @property decorator? >> > > > @property is super normal Python stuff that's in all the Python tutorials > and is something everyone should use all the time. > > @hybrid_property is more of a magic trick that's specific to the kind of > query interface that SQLAlchemy has - in that in an ORM like SQLAlchemy > (and lots of others), you access attributes off of classes, as well as > instances of those classes, as part of regular use of the API. This is not > a standard object-oriented thing, it's kind of odd. The @hybrid_property > allows you to build functions that act a lot like @property, but they > accommodate for accessing an attribute both at the "instance" (e.g. 'self') > level and at the "class" level. Which translated to SQLAlchemy means, at > the "row I've loaded into memory" level and the "SQL expression I want to > execute on the database" level. The kinds of functions we can use in these > two very different contexts are quite different. > > > > > > > >> Greg-- >> >> >> On Wed, Jun 7, 2017 at 5:08 PM, mike bayer <mike...@zzzcomputing.com >> <mailto:mike...@zzzcomputing.com>> wrote: >> >> >> >> On 06/07/2017 02:31 PM, GMS wrote: >> >> I am sure this is easier than I am making it, but I just want to >> add a property to a class so that decimal representations get >> truncated at 3 decimal digits. >> >> My class is this: >> >> class Measures(Model): >> __tablename__= 'xcelera_measures' >> id= Column(Numeric,primary_key=True) >> studyidk= Column(Numeric, ForeignKey('xcel.studyidk')) >> xceleragroup= relationship("Xcelera") >> explainstring= Column(String(255)) >> mrn= Column(String(255)) >> value= Column(Numeric) >> >> __mapper_args__= { >> "order_by": [mrn] >> } >> >> >> and 'value' is the property/attribute that I want to also have a >> truncated version available in the class. >> >> I tried adding this to the class value_new = >> column_property("%.3f" % value()) >> >> but got an error that >> >> value_new = column_property("%.3f" % value) >> >> >> "%" is a Python function, that doesn't execute on the database. >> This works as a normal Python descriptor: >> >> class MyClass(Base): >> # ... >> >> @property >> def value_new(self): >> return "%.3f" % self.value >> >> >> >> >> >> >> >> >> TypeError: float argument required, not Column >> >> I also tried this as a hybrid_property, but I don't think I was >> using it correctly. >> >> All I want to do is have the truncated version of my attribute >> available in my class. >> >> Thanks! >> >> Greg-- >> >> >> -- SQLAlchemy - >> The Python SQL Toolkit and Object Relational Mapper >> >> http://www.sqlalchemy.org/ >> >> To post example code, please provide an MCVE: Minimal, Complete, >> and Verifiable Example. See http://stackoverflow.com/help/mcve >> <http://stackoverflow.com/help/mcve> for a full description. >> --- >> 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 >> <mailto:sqlalchemy%2bunsubscr...@googlegroups.com> >> <mailto:sqlalchemy+unsubscr...@googlegroups.com >> <mailto:sqlalchemy%2bunsubscr...@googlegroups.com>>. >> To post to this group, send email to sqlalchemy@googlegroups.com >> <mailto:sqlalchemy@googlegroups.com> >> <mailto:sqlalchemy@googlegroups.com >> <mailto:sqlalchemy@googlegroups.com>>. >> Visit this group at https://groups.google.com/group/sqlalchemy >> <https://groups.google.com/group/sqlalchemy>. >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. >> >> >> -- SQLAlchemy - The Python SQL Toolkit and Object Relational >> Mapper >> >> http://www.sqlalchemy.org/ >> >> To post example code, please provide an MCVE: Minimal, Complete, and >> Verifiable Example. See http://stackoverflow.com/help/mcve >> <http://stackoverflow.com/help/mcve> for a full description. >> --- You received this message because you are subscribed to a topic >> in the Google Groups "sqlalchemy" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/sqlalchemy/3FFm1stwEoU/unsubscribe >> <https://groups.google.com/d/topic/sqlalchemy/3FFm1stwEoU/unsubscribe >> >. >> To unsubscribe from this group and all its topics, send an email to >> sqlalchemy+unsubscr...@googlegroups.com >> <mailto:sqlalchemy%2bunsubscr...@googlegroups.com>. >> To post to this group, send email to sqlalchemy@googlegroups.com >> <mailto:sqlalchemy@googlegroups.com>. >> Visit this group at https://groups.google.com/group/sqlalchemy >> <https://groups.google.com/group/sqlalchemy>. >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. >> >> >> >> >> -- >> Greg M. Silverman >> >> › flora-script <http://flora-script.grenzi.org/> ‹ >> **› grenzi.org <http://grenzi.org/> › >> >> -- >> SQLAlchemy - >> The Python SQL Toolkit and Object Relational Mapper >> >> http://www.sqlalchemy.org/ >> >> To post example code, please provide an MCVE: Minimal, Complete, and >> Verifiable Example. See http://stackoverflow.com/help/mcve for a full >> description. >> --- >> 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 <mailto: >> sqlalchemy+unsubscr...@googlegroups.com>. >> To post to this group, send email to sqlalchemy@googlegroups.com <mailto: >> sqlalchemy@googlegroups.com>. >> Visit this group at https://groups.google.com/group/sqlalchemy. >> For more options, visit https://groups.google.com/d/optout. >> > > -- > SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > description. > --- You received this message because you are subscribed to a topic in the > Google Groups "sqlalchemy" group. > To unsubscribe from this topic, visit https://groups.google.com/d/to > pic/sqlalchemy/3FFm1stwEoU/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at https://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. > -- Greg M. Silverman › flora-script <http://flora-script.grenzi.org/> ‹ › grenzi.org › -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- 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 https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
