<hasMany> tag

Description

The hasMany tag defines a relationship where an object has more than one of the child object specified by this tag. For example, a User might have several addresses.

There are two ways that hasMany relationships can be configured. The first is just like hasOne relationships except in the opposite direction. Rather than the parent object having a foreign key to the child object, the child object has the foreign key to the parent. To clarify, in your database you may have Customer table and an Address table with the following structure:

Customer Table

Name	Type	Nullable	Default	Other
customerId	Int	No		PK / Identity
username	Varchar(50)	No
password	Varchar(50)	No
firstName	Varchar(50)	No
lastName	Varchar(50)	No
dateCreated	DateTime	No	getDate()

Address Table

Name	Type	Nullable	Other
addressId	Int	No	PK / Identity
customerId	Int	No	FK to Customer.customerId
street1	Varchar(50)	No
street2	Varchar(50)	Yes
city	Varchar(50)	No
state	Varchar(50)	No
zip	Varchar(10)	No

Without any configuration, an instance of a Customer Record will automatically have getters and setters for each of the fields in the table. However, with a little extra configuration you tell Reactor that your Customer has many Addresses by virtue of the customerId field in both tables. Here is an example of that configuration:

Now, when you generate the Customer Record it will not have these additional method:

getAddressIterator() - This method returns an Iterator of Addresses related to the Customer. Iterators are objects which hold collections of records.

Note: All reactor generated methods with return objects lazy load the object. In other words the Iterator object is not instantiated until you call getAddressIterator(). Additionally these objects are cached. Calling getAddressIterator() two times will return the same instance of the Address Iterator.

The hasMany tag has one child tag, relate, which specify the fields which relate the two objects. You can nest multiple relate tags to indicate that the relationship between the objects depends on multiple fields. For example:

This example shows that the Customer is related by two columns to the Address, addressId and fooId which exist in both tables. This feature is useful when you have compound foreign keys defined in your database.

The other type of hasMany relationships are called linking relationships. These are used to gain objects which are related via another object. For example, it's common to have a CustomerAddress table which relates Customers to Addresses. This type of configuration in databases is frequently called a many to many relationship. Here's an example database structure:

Customer Table

Name	Type	Nullable	Default	Other
customerId	Int	No		PK / Identity
username	Varchar(50)	No
password	Varchar(50)	No
firstName	Varchar(50)	No
lastName	Varchar(50)	No
dateCreated	DateTime	No	getDate()

UserAddress Table

Name	Type	Nullable	Other
userAddressId	Int	No	PK / Identity
customerId	Int	No	FK to Customer.customerId
addressId	Int	No	FK to Address.addressId

Address Table

Name	Type	Nullable	Other
addressId	Int	No	PK / Identity
street1	Varchar(50)	No
street2	Varchar(50)	Yes
city	Varchar(50)	No
state	Varchar(50)	No
zip	Varchar(10)	No

This type of table structure allows for multiple addresses to be related to multiple customer and vice versa.

In this type of situation you would define the linking object to have one of both the related objects. The parent object would have many of the child object via a link though the linking object. This link is accomplished with the link tag.

Here's an example:

Now, when you create a Customer Record the object will have a getAddressIterator() method which will return an Iterator of address objects related to the Customer via the CustomerAddress table.

The hasMany tag has an optional alias argument. When not provided the alias defaults to the value of the name attribute. The alias argument controls how the methods generated from the relationship are named. For example, in the example above the Customer object hasMany Address objects. This causes the method name getAddressIterator() to be returned. If you wanted to rename this method to something else you can provide an alias on the relationship tag. If you provided an alias of "Location" the generated method would be named getLocatinIterator().

Unlike the relate tag, you can express multi-step relationships by providing multiple link tags.

Attributes

Attribute	Required	Description
name	yes	The alias of the related object. Note: If you did not specify an alias for the object that you are relating to, the alias is defaulted to the object's name.
alias	no	The alias to assign to this relationship. When not provided this defaults to the value of the name attribute.

Attribute

Required

Description

name

yes

The alias of the related object.

Note: If you did not specify an alias for the object that you are relating to, the alias is defaulted to the object's name.

alias

The alias to assign to this relationship. When not provided this defaults to the value of the name attribute.

Child tags

Tag	Required	Description
relate	yes (if a link is not provided)	Defines what fields that relate this object to the related object.
link	yes (if a relate is not provided)	Defines the object which links this parent object to its child.

Example