NAME¶
UR::Manual::Cookbook - Recepies for getting things working
Database Changes¶
Synchronizing your classes to the database schema¶
From under your application's Namespace directory, use the command-line tool
ur update classes
This will load all the data sources under the DataSource subdirectory of the
Namespace, find out what has changed between the last time you ran update
classes (possibly never) and now, save the current database schema information
in the Namespace's MetaDB, and update the class definitions for any changed
entities.
Possible conflicts¶
Avoid tables called 'type' or 'types'. It will conflict with the class metadata
class names where their class names end in '::Type'. The 'ur update classes'
tool will rename the class to 'YourNamespace::TypeTable' to avoid the
conflict, while keeping the table_name the same.
A table with multiple primary keys should not have one of them called 'id'. This
will result in a conflict with the requirement that a class must have have a
property called 'id' that uniquely identifies a member.
Relationships¶
Class relationships provide a way to describe how one class links to another.
They are added to a class by creating a property that lists how the class'
properties relate to each other.
There are two basic kinds of relationships: forward and reverse, Forward
relationships are used to model the has-a condition, where the primary class
holds the ID of the related class's instance. Reverse relationships are used
when the related class has a property pointing back to the primary class. They
are usually used to model a has-many situation where the related class holds
the ID of which primary class instance it is related to.
Has-a (One-to-one)¶
The container class/table has a foreign key pointing to a contained class/table
as in
table Container
column type constraint
----------------------------------------
container_id Integer primary key
value Varchar not null
contained_id Integer references contained(contained_id)
table Contained
column type constraint
----------------------------------------
contained_id Integer primary key
contained_value Varchar not null
Adding a forward relationship involves creating a property where the 'is' is the
name of the related class, and an 'id_by' indicating which property on the
primary class provides the foreign key with the related class' ID.
The class definition for the container would look like this:
class TheNamespace::Container {
table_name => 'container',
id_by => [
container_id => { is => 'Integer' },
],
has => [
value => { is => 'Varchar' },
],
has_optional => [
contained_id => { is => 'Integer' },
contained => { is => 'TheNamespace::Contained',
id_by => 'contained_id' },
],
data_source => 'TheNamespace::DataSource::TheDatabase',
};
If there was a NOT NULL constraint on the contained_id column, then the
contained_id and contained properties should go in the "has"
section.
And now for the contained class. We'll also include a reverse relationship
pointing back to the container it's a part of.
class TheNamespace::Contained {
table_name => 'contained',
id_by => [
contained_id => { is => 'Integer' },
],
has => [
container => { is => 'TheNamespace::Container',
reverse_as => 'contained',
is_many => 1 },
contained_value => { is => 'Varchar' },
],
data_source => 'TheNamsapce::DataSource::TheDatabase',
};
Note that the reverse_as parameter of the container property actually points to
the object accessor, not the id accessor. It doesn't make sense, but that's
how it is for now. Hopefully we'll come up with a better syntax.
Has-many¶
The contained class/table has a foreign key pointing to the container it's a
part of.
table Container
column type constraint
------------------------------------------
container_id Integer primary key
value Varchar not null
table Contained
column type constraint
------------------------------------------
contained_id Integer primary key
contained_value Varchar not null
container_id Integer references container(container_id)
To create a reverse relationship, you must first create a forward relationship
on the related class pointing back to the primary class. Then, creating the
reverse relationship involves adding a property where the 'is' is the name of
the related class, and a 'reverse_as' indicating which property on the related
class describes the forward relationship between that related class and the
primary class.
class TheNamespace::Container {
table_name => 'container',
id_by => [
container_id => { is => 'Integer' },
],
has => [
value => { is => 'Varchar' },
containeds => { is => 'TheNamespace::Contained',
reverse_as => 'container',
is_many => 1 },
],
data_source => 'TheNamespace::DataSource::TheDatabase',
};
class TheNamespace::Contained {
table_name => 'contained',
id_by => [
contained_id => { is => 'Integer' },
],
has => [
contained_value => { is => 'Varchar' },
container_id => { is => 'Integer' },
container => { is => 'TheNamespace::Container',
id_by => 'container_id' },
],
data_source => 'TheNamespace::DataSource::TheDatabase',
};
Many-to-many¶
Storing a has-many relationship requires a bridge table between the two main
entities.
table Container
column type constraint
--------------------------------------------
container_id Integer primary key
value Varchar not null
table Contained
column type constraint
--------------------------------------------
contained_id Integer primary key
contained_value Varchar not null
container_id Integer references container(container_id)
table Bridge
column type constraint
--------------------------------------------
container_id Integer references container(container_id)
contained_id Integer references contained(contained_id)
primary key(container_id,contained_id)
Here, both the Container and Contained classes have accessors to return a list
of all the objects satisfying the relationship through the bridge table.
class TheNamespace::Container {
id_by => [
container_id => { is => 'Integer' },
],
has => [
value => { is => 'Varchar' },
],
has_many => [
bridges => { is => 'TheNamespace::Bridge',
reverse_as => 'container' },
containeds => { is => 'TheNamespace::Contained',
via => 'bridge',
to => 'contained' },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
class TheNamespace::Bridge {
id_by => [
container_id => { is => 'Integer' },
contained_id => { is => 'Integer' },
],
has => [
container => { is => 'TheNamespace::Container',
id_by => 'container_id' },
contained => { is => 'TheNamespace::Contained',
id_by => 'contained_id' },
],
table_name => 'bridge',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
class TheNamespace::Contained {
id_by => [
container_id => { is => 'Integer' },
],
has => [
contained_value => { is => 'Varchar' },
],
has_many => [
bridges => { is => 'TheNamespace::Bridge',
reverse_as => 'contained' },
containers => { is => 'TheNamespace::Container',
via => 'bridge',
to => 'container' },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
Indirect Properties¶
Indirect properties are used to add a property to a class where the data is
actually stored in a direct property of a related class.
Singly-indirect¶
As in the has-a relationship, and the container class wants to have a property
actually stored on the contained class. Using the same schema in the has-a
relationship above, and we want the contained_value property to be accessible
from the container class.
class TheNamespace::Container {
id_by => [
container_id => { is => 'Integer' },
],
has => [
# This implies a contained_id property, too
contained => { is => 'TheNamespace::Contained',
id_by => 'contained_id' },
contained_value => { via => 'contained',
to => 'contained_value' },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
You can now use "contained_value" as an accessor on
TheNamespace::Container objects. You can also use "contained_value"
as a parameter in "get()", and the underlying data source will use a
join if possible in the SQL query.
Many Singly-indirect¶
As in the singly-indirect recipe, but the container-contained relationship is
has-many
class Container {
id_by => [
container_id => { is => 'Integer' },
],
has => [
containeds => { is => 'TheNamespace::Contained',
reverse_as => 'container',
is_many => 1 },
contained_values => { via => 'containeds',
to => 'container_value',
is_many => 1 },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
Doubly-indirect¶
If you have a normal has-a relationship between a container and a contained
item, and the contained item also has-a third-level contained thing, and you'd
like to have a property of the innermost class available to the first
container:
class Container {
id_by => [
container_id => { is => 'Integer' },
],
has => [
contained => { is => 'TheNamsepace::Contained',
id_by => 'contained_id '},
inner_contained => { is => 'TheNamespace::InnerContained,
via => 'contained',
to => 'inner_contained_id' },
inner_contained_value => { via => 'inner_contained',
to => 'inner_contained_value' },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
Many doubly-indirect¶
Combining the has-many relationship and the doubly indirect recipe
class Container {
id_by => [
container_id => { is => 'Integer' },
],
has => [
containeds => { is => 'TheNamsepace::Contained',
reverse_as => 'container',
is_many => 1},
inner_containeds => { is => 'TheNamespace::InnerContained,
via => 'contained',
to => 'contained',
is_many => 1 },
inner_contained_values => { via => 'inner_containeds',
to => 'inner_contained_value',
is_many => 1 },
],
table_name => 'container',
data_source => 'TheNamespace::DataSource::TheDatabase',
};
And then you get an accessor inner_containeds to return a list of
inner-contained objects, and another accessor inner_contained_values to return
a list of their values.