one to many relationships in different columns - sql

Question

This is newbee SQL question I struggled to find a clear answer to. So please help. I have two tables in database with fields as listed below:
ConstructionProjects
id (unique, nonempty)
developer (one, nonempty)
main_contractor (one, nonempty)
architect (one, nonempty)
(other fields)
Companies
id (unique, nonempty)
projects_developed (many or none)
projects_as_main_contractor (many or none)
projects_as_architect (many or none)
(other fields)
So every project has only one developer, one architect and one contractor, however, it may be the same company. Any company may be involved in as many projects in any roles.
Is there a way to avoid creating 3 additional association tables to establish many to many relationships? and make 3 one to many relationships instead?
If so, which practice is better?
*In other words, I don't understand relationships (one to many and many to many) relate (1) row to row or (2) row to "specific cell"?
(1) if row to row then I have many to many relationships
(2) if row to specific cell then it is multiple one to many relationships...*
I'm learning Flask_alchemy and PostgreSQL.
I ran into problem, writing a code like this (there's no reference to specific columns between tables). So this is not ok?
class Company(db.Model):
id = db.Column(db.Integer, primary_key = True)
constr_projects_developed = db.relationship('ConstrProject', backref='developer')
constr_projects_main_contracts = db.relationship('ConstrProject', backref='main_contractor')
constr_projects_architect = db.relationship('ConstrProject', backref='architect')
class ConstrProject(db.Model):
id = db.Column(db.Integer, primary_key = True)
developer_id = db.Column(db.Integer, db.ForeignKey('company.id'))
main_contractor_id = db.Column(db.Integer, db.ForeignKey('company.id'))
architect_id = db.Column(db.Integer, db.ForeignKey('company.id'))
Then my question is, the correct way to do it is like this (1):
class Company(db.Model):
id = db.Column(db.Integer, primary_key = True)
constr_projects_developed = db.relationship('ConstrProject', back_populates='developer')
constr_projects_main_contracts = db.relationship('ConstrProject', back_populates='main_contractor')
constr_projects_architect = db.relationship('ConstrProject', back_populates='architect')
class ConstrProject(db.Model):
id = db.Column(db.Integer, primary_key = True)
developer_id = db.Column(db.Integer, db.ForeignKey('company.id'))
developer = db.relationship('Company', back_populates='constr_projects_developed')
main_contractor_id = db.Column(db.Integer, db.ForeignKey('company.id'))
main contractor = db.relationship('Company', back_populates='constr_projects_main_contracts')
architect_id = db.Column(db.Integer, db.ForeignKey('company.id'))
architect = db.relationship('Company', back_populates='constr_projects_architect')
Or like this(2)?:
class Company(db.Model):
id = db.Column(db.Integer, primary_key = True)
cp_developed = db.relationship('Company', secondary=cp_developer_company, back_populates='developer')
cp_main_contracts = db.relationship('Company', secondary=cp_main_contractor_company, back_populates='main_contractor')
cp_architects = db.relationship('Company', secondary=cp_architect_company, back_populates='architect')
class ConstrProject(db.Model):
id = db.Column(db.Integer, primary_key = True)
developer = db.relationship('Company', secondary=cp_developer_company, back_populates='cp_developed')
main_contractor = db.relationship('Company', secondary=cp_main_contractor_company, back_populates='cp_main_contracts')
architect = db.relationship('Company', secondary=cp_architect_company, back_populates='cp_architects')
cp_developer_company = db.Table('cp_developer_company'
db.Column('company_id', db.Integer, db.ForeignKey('company.id'))
db.Column('constr_project_id', db.Integer, db.ForeignKey('constrproject.id'))
)
cp_main_contractor_company = db.Table('cp_main_contractor_company'
db.Column('company_id', db.Integer, db.ForeignKey('company.id'))
db.Column('constr_project_id', db.Integer, db.ForeignKey('constrproject.id'))
)
cp_architect_company = db.Table('cp_architect_company'
db.Column('company_id', db.Integer, db.ForeignKey('company.id'))
db.Column('constr_project_id', db.Integer, db.ForeignKey('constrproject.id'))