Mapping two loops into a single loop - 8.0

Talend Data Mapper User Guide
Version
8.0
Language
English
Product
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Module
Talend Studio
Content
Design and Development > Designing Jobs
Last publication date
2024-03-28
Merge two parallel loops into a single loop using an aggregation function.

Before you begin

You have created a map with an input and output structure. For this example, you can use CustomerAddress as input and CustomerCombinedAddresses as output. These structures can be found under Other Projects > Examples > Structures > Simple > Customer.

About this task

In this example, you have an input with two loops: Address and AddressDetail, and you want to map their elements to a single Address loop in the output.

This map is available in Other Projects > Examples > Maps > Looping > LoopMergeTwoLoops.

Procedure

  1. Drag the input Address loop to the corresponding output loop.
    The elements are mapped and a looping expression is added to the output Address.
  2. Drag the input Detail element to the corresponding output.
  3. In the dialog box that opens, click Yes.
    An AgConcat with a loop expression and context is automatically created. If you test the map, the output Detail element will contain all the values in the input element, for every iteration of the Address element. If you want to have the value of only one Detail iteration, you need to use a filter.
  4. Drag and drop a SingleIndex function the Filter argument of the looping expression under the NestedContext function.
  5. Drag and drop a LoopIndex function on the Index argument.
  6. Drag and drop the output Address element on the Looping Output Element argument.
    This specifies that the Detail element should return only one value per iteration, based on the index of the Address loop. For example, for the first iteration of Address, the output Details returns the value of the input Details for the first iteration of AddressDetails.

Results

The elements are mapped, you can use the Test Run button to see the output based on the sample input file. In this example, the output looks like this:
<Customer>
  <Address>
    <Detail>Information about 123 Main Street</Detail>
    <Street>123 Main Street</Street>
    <City>Oakland</City>
    <State>CA</State>
  </Address>
  <Address>
    <Detail>Information about 456 Broadway Ave</Detail>
    <Street>456 Broadway Ave</Street>
    <City>Oakland</City>
    <State>CA</State>
  </Address>
  <Address>
    <Detail>Information about 67th Street</Detail>
    <Street>912 67th Street</Street>
    <City>Berkeley</City>
    <State>CA</State>
  </Address>
  <Address>
    <Detail>Information about 415 East Ave</Detail>
    <Street>415 East Ave</Street>
    <City>Oakland</City>
    <State>CA</State>
  </Address>
</Customer>