What You May Need to Know About the Assign Activity

Note the following issues about the assign activity.

The assign activity is executed in the order of the <copy> elements that appear in the Mediator mplan.
You can reorder the assignments by selecting an assignment in the bottom pane of the Assign Values dialog and clicking the Up or Down arrow to move the assignment in the assignments list.
When creating a new assignment, you can choose to insert it at the desired place in the list of assignments. Select an existing assignment in the bottom pane of the Assign Values dialog and select Insert New Rule After or Insert New Rule Before from the list at the top left of the dialog.
The output variable from the Translate From Native activity and the input variable to a Translate To Native activity are also available for assignments in the Assign Values dialog.
All assignments that appear in the bottom pane of the Assign Values dialog are applied to the Mediator mplan only after you click OK.
A source XPath expression should always refer to a leaf node while the source is assigned to a target property. Otherwise, all the values of the child nodes in the source get concatenated and are assigned to the target property. The following example provides details:
```
<copy target="$out.property.jca.file.FileName"
 expression="$in.body/imp1:request/ProductReq/Make"
 xmlns:imp1="http://xmlns.oracle.com/psft"/>
```
Note:

A leaf node is a node with no child nodes.
While assigning a constant or a property to a target XPath expression, the target XPath expression should always point to a leaf node. Otherwise, nonleaf nodes contain only a string value that may generate nonvalid XML according to the .xsd file. The following example provides details.
```
<copy target="$out.request/inp1:request/ProductReq/Make" value="NewMakeValue"
 xmlns:inp1="http://xmlns.oracle.com/psft"/>
```
In this example, $out.request/inp1:request/ProductReq/Make refers to the leaf node.
If a transformation is available, then while assigning a source part to a target part, the target is overwritten because the assign activity occurs on top of the transformation. If the transformation is not available, then the assign activity creates the target. The following example provides details.
```
<copy target="$out.request" expression="$in.body"/>

<copy target="$out.header.inp1_header" expression="$in.header.inp1_header"
  xmlns:inp1="http://xmlns.oracle.com/psft"/>
```
If one of the child nodes in the target payload has to be modified, then there are the following two use cases:
- If a transformation is available, then directly assign a source expression to a target XPath expression that is pointing to that child node in the target. The following example provides details:
```
<copy value="ConstantModel"
target="$out.request/inp1:request/ProductReq/Model"
 xmlns:inp1="http://xmlns.oracle.com/psft"/>
```
- If a transformation is not available, then there are two steps involved. First, assign the source part to the target part, and then assign the source expression to a target XPath expression that is pointing to the child node in the target. The following example provides details:
```
<copy target="$out.request" expression="$in.body"/> and <copy
 value="ConstantModel" target="$out.request/inp1:request/ProductReq/Model"
 xmlns:inp1="http://xmlns.oracle.com/psft"/>
```
When only one of the child nodes of the source has to be propagated into a target, then first ensure that there is no transformation invoked. Then, assign the source XPath expression to point to the required child node. The following example provides details:
```
<copy target="$out.request/imp1:ProductReq"
 expression="$in.body/imp1:request/ProductReq"
 xmlns:imp1="http://xmlns.oracle.com/psft"/>
```
In this case, the source element evaluated from $in.body/imp1:request/ProductReq does not contain a complete tree structure that starts from the root element, but contains only a child node. The following example provides details:
```
<ProductReq>
        <Make>MAKE</Make>
        <Model>MODEL</Model>
</ProductReq>
```
If there are multiple assign activities in a Mediator and each source XPath expression points to a different child node, then there are the following two use cases:
- If a transformation is available, then the corresponding child node in the target is updated.
- If a transformation is not available, then the target should be a multiple part target with each part referring to the source child node.
With headers, if the passThroughHeader property is set, then
- Any header manipulation in a transformation is updated in the target headers.
- The part level assign activity overwrites the target header part.
- The below part level node assign activity updates the corresponding node in the target.
If multiple source nodes (below part level) are assigned to the same target node (below part level), then the target node contains the value of the last copy element in the assign activity. The following example provides details.
```
<copy target="$out.request/imp1:request/ProductReq/Make"
 expression="$in.body/imp1:request/ProductReq/Model"
xmlns:imp1="http://xmlns.oracle.com/psft"/>

<copy target="$out.request/imp1:request/ProductReq/Make"
 expression="$in.body/imp1:request/Description"
xmlns:imp1="http://xmlns.oracle.com/psft"/>
```
In the preceding example, the first copy element does not have any effect because the second copy element overwrites it.
If the XPath expression results in a list (multiple occurrences), then there are the following two use cases:
- If the list contains a single element, then the XPath expression is propagated.
- If the list contains multiple elements, then the XPath expression is not supported.
The following activities happen while assigning a source child node to a target child node:
1. The source child node name and namespace are overwritten by the target node name and namespace, respectively.
2. The target child node is replaced by the source child node in the parent node of the target node.