<join> Examples

<join> Examples

Defining Join Conditions

You use the joincondition attribute and outputvariable to define a basic <join> statement.

The following example is a simple join of two variables based on a single condition. For clarity, the data for the variables is shown directly. The joincondition attribute contains an XPath expression that defines the single condition:

<variable name="movies" type="document">
<movies>
<movie id="Stargate" ... />
<movie id="Lassie" ... />
...
</movies>
</variable>
<variable name="reviews" type="document">
<reviews>
<review>
<title>Encounters of the Third Kind</title>
<rating>4</rating>
...
</review>
<review>
<title>Stargate</title>
<rating>4.5</rating>
...
</review>
...
</reviews>
</variable>
<join outputvariable="$joinResult"
joincondition="$movies/movies/movie/@id =
$reviews/reviews/review/movie/title"/>

Each condition consists of an XPath expression, identifying a node for one item, a comparison operator and another XPath expression, identify the node for a related item to be joined. You can also use XPath functions in these XPath expressions.

Note: In earlier versions, XPath expression within the join condition did not have to contain the root node, such as $movies/movie/@id instead of $movies/movies/movie/@id. The previous syntax is no longer supported and will fail.

Valid Join Operators

You can use any of the basic math comparison operators (= , !=, <, <=, >, and >=). For string comparisons, you can also use ~ to express a partial match relationship. Comparisons with ~ are not case sensitive.

You must use XML escaping with operators that include < or > characters. See XML Escaping in URLs and Expressions for more information.

The following example would join an item from the location variable to items in the companyProfiles variable as long as the location city name is contained within the company profile address:

Defining Multiple Conditions

You can combine two or more conditions in the joincondition attribute using the logical XPath keywords and or or. You cannot use parentheses or other grouping symbols to define precedence, however. The joincondition attribute only supports very straightforward joins.

Selecting Nodes for Joined Items with <select>

The <select> element is an optional child for <join>. It allows you to define the structure of the joined items to return and selectively choose which nodes to include. If you omit <select> all the nodes from the join data are included in the output.

To define the resulting structure for the output variable:

Define the name of the root node that encloses all results inthe name attribute of <select>.

Define the structure for each row or item in the result asliteral XML in the body of <select>. This structure must contain:

The root node to wrap each repeating item from the <join> operation.

The descendant nodes to include within each item.

This result structure also contains mashup expressions thatdetermine what joined data will be selected to fill the result. See Dynamic Mashup Expressions for moreinformation.

Note: Previous versions of MashZone NextGen required you to wrap CDATA sections around the contents of <select>. CDATA is a deprecated technique. Instead, declare a result namespace on <mashup> and use this namespace to identify the output.

In the next example, the output variable will contain a <res:recommendations> element with a repeating set of <res:movie> children - the repeating items. Each <res:movie> contains a <res:movietitle> child with data from the variable named movies and <res:rating> and <res:comment> children with data from the variable named reviews.

<join outputvariable="$joinResult"
joincondition="$movies/movie/@id = $reviews/review/movie/title">
<select name="res:recommendations">
<res:movie>
<res:movietitle>{$movies/title}</res:movietitle>
<res:rating>{$reviews/rating}</res:rating>
<res:comment>{$reviews/comment}</res:comment>
</res:movie>
</select>
</join>

Working Samples

The following sample mashups use the <join> statement:

CompanyInfoJoinSample (join.emml)

CompanyInvokeJoinSample(joinfunctions.emml)

JoinUsingMatches (joinmatches.emml)

PortfolioJoine (joinselect.emml)

See Mashup Samples for a list of MashZone NextGen mashup samples and where to find them.