Defining collection in items.xml

Collection basically contains the elements of element type.
element type means the type of elements we are adding into the collection.

Example:
Collection of String will contain the elements of String element type.
Collection of Integer will contain the elements of Integer type.
Collection of Address will contain the elements of Address type.

Note:

Element type can be a simple atomic type or it can be any other complex type.

We define collection of string as below

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<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false"/>
<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false"/>

We have not specified the type,so it takes Collection of String by default.

We define List of string as below

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<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false" type="list"/>
<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false" type="list"/>

We have specified type=list so It will be List of String.

We define Set of string as below

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<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false" type="set"/>
<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false" type="set"/>

In all the above definitions, elementtype is String which is an atomic type

We define Collection of Address as below

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<collectiontype code="AddressCollection" elementtype="Address" autocreate="true" generate="false"/>
<collectiontype code="AddressCollection" elementtype="Address" autocreate="true" generate="false"/>

Here elementtype is Address which is a complex type and also another item type.

We define List of Language as below

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<collectiontype code="LanguageList" elementtype="Language" autocreate="true" generate="true" type="list"/>
<collectiontype code="LanguageList" elementtype="Language" autocreate="true" generate="true" type="list"/>

Here elementtype is Language which is a again another item type

How we use these collections with item type?

Once we have created the collection, we need to inject them to the required item type.

We can inject list of language and list of String to our CustomUser type as below

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<itemtype code="CustomUser" autocreate="true" generate="false">
                <deployment table="CustomUser" typecode="11001" />
                <attributes>
                    <attribute qualifier="userId" type="java.lang.String">
                        <modifiers optional="false" unique="true"/>
                        <persistence type="property" />
                    </attribute>
                    <attribute qualifier="languages" type="LanguageList">
                        <modifiers unique="false" read="false"/>
                        <persistence type="property" />
                    </attribute>
                    <attribute qualifier="nickNames" type="StringCollection">
                        <modifiers unique="false" read="false"/>
                        <persistence type="property" />
                    </attribute>
                </attributes>
            </itemtype> 
<itemtype code="CustomUser" autocreate="true" generate="false">
				<deployment table="CustomUser" typecode="11001" />
				<attributes>
					<attribute qualifier="userId" type="java.lang.String">
						<modifiers optional="false" unique="true"/>
						<persistence type="property" />
					</attribute>
					<attribute qualifier="languages" type="LanguageList">
						<modifiers unique="false" read="false"/>
						<persistence type="property" />
					</attribute>
					<attribute qualifier="nickNames" type="StringCollection">
						<modifiers unique="false" read="false"/>
						<persistence type="property" />
					</attribute>
				</attributes>
			</itemtype> 

We can see that 2nd attribute has a qualifier called “languages”
And its type is “LanguageList” which is basically the code we defined in the collection of Language using below tag

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<collectiontype code="LanguageList" elementtype="Language" autocreate="true" generate="true" type="list"/> 
<collectiontype code="LanguageList" elementtype="Language" autocreate="true" generate="true" type="list"/> 



We can see that 3rd attribute has a qualifier called “nickNames”
And its type is “StringCollection” which is basically the code we defined in the collection of String using below tag

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<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false"/>
<collectiontype code="StringCollection" elementtype="java.lang.String" autocreate="true" generate="false"/>

The code in the collectiontype tag should become the type for an attribute in the attribute definition.

After adding this change in items.xml file, do the build

CustomUserModel.java file will be generated
Check this file for the attribute called “languages” and “nickNames”

It should be generated as below

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private List<LanguageModel> _languages;
private Collection<String> _nickNames;
private List<LanguageModel> _languages;
private Collection<String> _nickNames;

So we have defined List of langauge and a collection of String for CustomUserModel.

While defining collection,
make autocreate as true so that collection type gets created in the backend.
make generate as false as we don’t need to generate Jalo class for collection type.

How collection will be stored in DB ?


There are 2 cases in Collection

1)Collection of Atomic type
In our CustomUser item type we have defined List of nickName Where nickName is a String which is atomic type.

If collection contains atomic types then the values are stored as binary fields in the database.

2)Collection of Non atomic/composed type
In our CustomUser item type we have defined List of Language Where Language is a separate item type.

If collection contains complex types then those items PKs are stored as one single String separated by comma for each PK in the database.

About the Author

Karibasappa G C (KB)
Founder of javainsimpleway.com
I love Java and open source technologies and very much passionate about software development.
I like to share my knowledge with others especially on technology 🙂
I have given all the examples as simple as possible to understand for the beginners.
All the code posted on my blog is developed,compiled and tested in my development environment.
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