Hi Simon, thanks for the help! I've never used that before, it's quite handy.
I'm looping through all the students and printing them and their subject details to a CSV file. What makes things a tad complicated is the subjects must appear in a specific order. There is a table that has the subject code and order number (ordered_subjects used below is the resultset from it). I printed out the timing and found the problem to be with a nested for loop. I was hoping to reduce that process time by using a map that automatically gets populated instead of having to create it on the fly. Before - subjects_collection "attribute_mapped_collection": ******************************************************************************************** for row in students: row_no += 1 for subject in row.subjects: student_subjects[subject.code] = subject.value csv_row = [row_no] csv_row += [student_subjects.get(x.code, '') for x in ordered_subjects] csv_row += [row.created_on, row.updated_on] writer.writerow([x.encode('utf-8') if type(x) == unicode else x for x in csv_row]) After adding the subjects_collection "attribute_mapped_collection", I unfortunately did not see a change in performance. After - subjects_collection "attribute_mapped_collection": ******************************************************************************************** for row in students: row_no += 1 csv_row = [row_no] csv_row += [row.subjects_collection.get(x.code, '').value for x in ordered_subjects] csv_row += [row.created_on, row.updated_on] writer.writerow([x.encode('utf-8') if type(x) == unicode else x for x in csv_row]) class Subject(db.Model): __tablename__ = 'subjects' student_id = db.Column(db.Integer, db.ForeignKey('students.id'), primary_key=True) code = db.Column(db.String(50), primary_key=True) value= db.Column(db.String) def __init__(self, code , value): self.code = code self.value = value class Student(ResourceMixin, db.Model): __tablename__ = 'students' subjects= db.relationship('Subject', backref='student') id = db.Column(db.Integer, primary_key=True) subjects_collection = relationship("Subject", collection_class=attribute_mapped_collection('code')) Can you see a way I can optimize this? Any ideas? On Friday, 3 July 2020 12:31:03 UTC+2, Simon King wrote: > > Are you trying to optimise the database access (ie. minimize the > number of queries), or provide a nice dictionary-style API for your > Student objects? What do you mean when you say that looping over > student.subjects is quite heavy? > > An association proxy can be used to get dict-style access to a > relationship: > > > https://docs.sqlalchemy.org/en/13/orm/extensions/associationproxy.html#proxying-to-dictionary-based-collections > > > There are also a couple of examples in the SQLAlchemy docs that > provide a dictionary-style API: > > > https://docs.sqlalchemy.org/en/13/orm/examples.html#module-examples.dynamic_dict > > > > https://docs.sqlalchemy.org/en/13/orm/examples.html#module-examples.vertical > > Hope that helps, > > Simon > > On Thu, Jul 2, 2020 at 8:46 PM Justvuur <just...@gmail.com <javascript:>> > wrote: > > > > Hi there, > > > > I'm struggling to find an efficient way to get a two columned subset > into dictionary form. > > > > I have an entity that has a subset of data. The subset is linked to the > entity via Id. The order of the subset of data is defined in another table. > > > > Example: > > Student - Id, firstname, lastname > > Subjects - StudentId, SubjectCode, SubjectName > > > > At the moment I'm looping through the SqlAlchemy result of > "student.subjects" in python and creating a dictionary from that. It's > quite heavy, especially when there are 2000+ students with a potential of > 100+ subjects each. > > > > For each student, how do I get the subjects as a dictionary for a > student where the key is the SubjectCode and the value is the SubjectName? > > Better yet, how can I get a result set: Id, firstname, lastname > SubjectCode x, SubjectCode y, etc etc (where the SubjectName becomes the > value and the SubjectCode becomes the column)? > > > > Regards, > > Justin > > > > -- > > 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 sqlal...@googlegroups.com <javascript:>. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/57b74c9a-a6e5-494b-b468-d0bdcbcce60co%40googlegroups.com. > > > -- 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. 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