referenceHasMetaData (metaDataKey)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

..	list-table:: 
	:widths: 20 80
	:header-rows: 0
	:class: tight-table

	*	-	Category
		-	metadata functions
	*	-	Signature
		-	referenceHasMetaData(String metadataKey, String metadataValue) : boolean
	*	-	Description
		-	Checks if the model reference in the context has a certain metadata key.
	*	-	Arguments
		-	metaDataKey: key of metadata to check for existence
	*	-	Returns
		-	- true if the model reference in the context has the metadata key
			- false if the model reference in the context does not have the metadata key
	*	-	Exceptions
		- .. error::
			This function raises a *No model reference in context* exception when the context does not contain a model reference.
	*	-	Example
		-	The following example shows a code instruction that generates a Java class for each object,
			and conditionally adds a field for each reference that has metadata *bar*. The field will have a comment line.
			
			Given the input shown in the input section below CodeComposer will generate the comment for reference *exampleObject2* and *exampleObject3* as shown in the output section below.

			.. note::
				Multiple code instructions may generate code in the same output file. The datatype of the fields shown in the output is generated by another code instruction.
			
			**Input**

			.. code-block:: xml
				:caption: src/codeinstruction/examples/example-code-instruction-simple-entity-foreach-reference-and-reference-has-meta-data.xml
				:name: ReferenceHasMetaData_CodeInstruction
				:linenos:
				:emphasize-lines: 13, 15
				
				<?xml version="1.0" encoding="UTF-8"?>
				<java_package xmlns="https://metafactory.io/xsd/v1/java-codeinstruction"
				              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
				              xsi:schemaLocation="https://metafactory.io/xsd/v1/java-codeinstruction https://metafactory.io/xsd/v1/java-codeinstruction.xsd"
				              name="${pattern.property.java.package.base}.entities.simple"
				              path="${pattern.property.java.main.directory}"
				              package="domain_model">
				  <class  name="${createSimpleEntityClassName(${object.name})}"
				          foreach="object">
				    <field  name="${reference.name}"
				            access="rw"
				            foreach="reference"
				            condition="${referenceHasMetaData(bar)}"
				    >
				      <apicommentline>${fmsnippet.examples.exampleCommentForReferenceThatHasMetaDataBar}</apicommentline>
				    </field>
				  </class>
				</java_package>

			.. code-block:: 
				:caption: src/snippet/examples/exampleCommentForReferenceThatHasMetaDataBar.ftl
				:name: ReferenceHasMetaData_Snippet1
				:linenos:
				:emphasize-lines: 3

				<#if !(modelReference)??>  <#stop "modelReference not found in context" ></#if>

				This is an example comment for a reference with meta data bar: ${modelReference.type} ${modelReference.name}. 
			
			.. code-block:: xml
				:caption: src/model/model.xml
				:name: ReferenceHasMetaData_Model
				:linenos:
				:emphasize-lines: 10, 11, 15, 20

				<?xml version="1.0" encoding="UTF-8"?>
				<model xmlns="https://metafactory.io/xsd/v1/model" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://metafactory.io/xsd/v1/model https://metafactory.io/xsd/v1/model.xsd">
					<package name="domain_model">
						<object name="ExampleObject4">
							<metadata>
								<name.plural>ExampleObjects4</name.plural>
								<serialVersionUID>0</serialVersionUID>
							</metadata>
							<reference name="exampleObject1" type="ExampleObject1" multiplicity="1..1" notnull="true">
								<metadata>
								</metadata>
							</reference>
							<reference name="exampleObject2" type="ExampleObject2" multiplicity="1..1" notnull="true">
								<metadata>
									<bar></bar>
								</metadata>
							</reference>
							<reference name="exampleObject3" type="ExampleObject3" multiplicity="1..1" notnull="true">
								<metadata>
									<bar>baz</bar>
								</metadata>
							</reference>
						</object>
					</package>
				</model>

			**Output**

			.. code-block:: java
				:caption: src/main/java/io/metafactory/codecomposer_reference/entities/simple/ExampleObject4SimpleEntity.java
				:name: GetMetaDataFromObject_Output1
				:linenos:
				:emphasize-lines: 8, 14
	
				package io.metafactory.codecomposer_reference.entities.simple;

				public class ExampleObject4SimpleEntity
				{
					private ExampleObject1SimpleEntity exampleObject1;

					/**
					 * This is an example comment for a reference with meta data bar: ExampleObject2 exampleObject2.
					 */
					private ExampleObject2SimpleEntity exampleObject2;
				
				
					/**
					 * This is an example comment for a reference with meta data bar: ExampleObject3 exampleObject3.
					 */
					private ExampleObject3SimpleEntity exampleObject3;
				}