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Modeling: User's Guide |  |
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Modeling: User's Guide | |
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RToOne objects describe a to-many relationship from an Entity to another. It derives from Relationship and overrides the following defaults:
| Prop. | Type | Default | Comment |
|---|---|---|---|
name |
string |
no default | The name is the only
mandatory arguments when instanciating a APrimaryKey. Once set, it
should not be changed |
multiplicity |
sequence | [0, None] |
None means
unconstrained: no upper limit |
joinSemantic |
int |
0 |
see 2.4.7 for possible values |
(All other defaults are BaseRelationship's ones, cf.2.4.7)
Minimally, a RToMany needs a name and a the name of the
destination entity, destination.
Attributes src and dst, identifying source and destination
attributes, are automatically calculated if they are not supplied. The rules
are the same than the ones given above for RToOne, you just need to
swap name 'src'/''source'' and 'dst'/''destination'' in the
above explanation.
As an example, suppose you have a pymodel declaring such a RToMany:
self.model.entities = [
Entity('Store',
properties=[RToMany('toEmployees','Employee')]
),
# ...
]
RToMany then automatically binds 'src' to the source entity
'Store' 's primary key, and creates a AForeignKey named
'fkStore' in the destination entity 'Employee' (unless such a
property -either an attribute or a relationship- already exists with this
name, in which case it uses the first unused name among 'fkStore1',
'fkStore2', etc.
You'll also want to read the section 2.4.7 for a complete explanation on how automatic binding/generation of APrimaryKey/AForeignKey is handled when two relationships are inverse of each other.
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Modeling: User's Guide | |
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