Hello friends,

In this article, we will see some simple and tricky use cases while dealing with selectors in mulesoft integration. This article is only focused on dataweave2 transformations and Mule4.

Dataweave selectors parse input messages and traverse the structure, evaluates it and return the desired output.

Let’s see some of the useful selectors which are covered as part of this article. Also, I have covered some useful scenarios by combining these selectors at the end of this article.

• Single-value
• Multi-value
• Descendants
• Key-value pair

Single-value Selector

For single value selector we can use .keyName syntax. It will return value for matching key.

Input Data

For single value selector check, lets consider a small data-set as given below. Here, I want to fetch the user name from the input.

XML
<users>
  <user>
    <name>Manish</name>    
  </user>
</users>

JSON
{
  "users": {
    "user": {
      "name": "Manish"
    }
  }
}

Single value Dataweave Selector code

Below dataweave expression will work on both input data format.

%dw 2.0
output application/json
---
payload.users.user.name

"Manish"

Multi-value Selector

Single value selector will return single value from the input data. If we have multiple keys with same name it will return first element from the list and will ignore rest of the entries. Here, Multi value selector (.*keyName) is useful and will return Array of values of any matching keys. We need to use * to retrieve multiple values.

Input Data

For Multi value selector check, lets consider a small data-set as given below. Here, I want to fetch the user name from the input. We have more than one keys with same key name “name”.

XML
<users>
  <user>
    <name>Hari</name> 
    <name>Manish</name>   
  </user>
</users>

Json
{
  "users": {
    "user": {
      "name": "Hari",
      "name": "Manish"
    }
  }
}

Multi-Value selector Dataweave code

Below dataweave expression will work on both input data format to retrieve all values against the key “name” at user level.

%dw 2.0
output application/json
---
payload.users.user.*name

Output

[
  "Manish",
  "Hari"
]

Descendants Selector

Descendant selector(..keyName) is very useful while retrieving all the values recursively from node level. It will return Array of values of any matching descendant keys.

Input Data

XML
<users>
  <user>
    <name>Manish</name>
    <user>
      <name>Hari</name>
      <user>
        <name>Niral</name>
      </user>
    </user>
  </user>
</users>

JSON
{
  "users": {
    "user": {
      "name": "Manish",
      "user": {
        "name": "Hari",
        "user": {
          "name": "Niral"
        }
      }
    }
  }
}

Descendants Dataweave code – 1st scenario

Below dataweave expression will work on both input data format to retrieve all values against the key “name” from the input payload.

%dw 2.0
output application/json
---
payload..name

Output
[
  "Manish",
  "Hari",
  "Niral"
]

Descendants Dataweave code – 2nd scenario

With below dataweave expression, if you see the output it is skipping first name entry “Manish” as descendant selector is used 2nd level or depth of the input.

%dw 2.0
output application/json
---
payload.users.user.user..name

Output
[
  "Hari",
  "Niral"
]

Key-value pair Selector

Key-value selector(.&keyName) is used to retrieve the object(key, value) against the matching key.

Input Data

XML
<users>
  <user>
    <name>Hari</name>
    <name>Manish</name>      
  </user>
</users>

JSON
{
  "users": {
    "user": {
      "name": "Hari",
      "name": "Manish"
    }
  }
}

Dataweave key-value pair code

%dw 2.0
output application/json
---
payload.users.user.&name

Output
{
  "name": "Hari",
  "name": "Manish"
}

Combining selectors

Now, lets see some usecase where we need to be extra careful while using these selectors. Lets consider the input below:

XML
<users>
  <user>
    <name>Manish</name>
    <user>
      <name>Preeti</name>
      <user>
        <name>Niral</name>
      </user>
      <name>Ramesh</name>
    </user>
    <name>Hari</name>
  </user>
</users>

JSON
{
  "users": {
    "user": {
      "name": "Manish",
      "user": {
        "name": "Preeti",
        "user": {
          "name": "Niral"
        },
        "name": "Ramesh"
      },
      "name": "Hari"
    }
  }
}

If we only use descendants selector with above input we will not get the proper results. It will select only first element from each node.

%dw 2.0
output application/json
---
payload..name

[
  "Manish",
  "Preeti",
  "Niral"
]

%dw 2.0
output application/json
---
payload..*name

Output

[
  "Manish",
  "Hari",
  "Preeti",
  "Ramesh",
  "Niral"
]

Similarly, if you want to get all the key-value pairs you need to combine key-value selector with descendants selector. It will retrieve all elements from each node and results the output as combined array.

%dw 2.0
output application/json
---
payload..&name

Output

[
  {
    "name": "Manish",
    "name": "Hari"
  },
  {
    "name": "Preeti",
    "name": "Ramesh"
  },
  {
    "name": "Niral"
  }
]

Some of common useful dataweave use-cases that you can check from our previous articles:

• Filter-complex-array-using-dw2-mule4
• how-to-lookup-csv-table-using-dw2
• pattern-matching-in-dw-using-match-case
• splitby-and-joinby-function-dataweave
• array-comparison-use-case-dw2
• dataweave-useful-string-functions-part1
• optimize-json-data-using-dataweave
• how-to-write-attributes-from-xml-to-json-dw2
• use-secure-properties-in-dw2

Also, there are a lot selectors available in Mulesoft docs which you can explore from here.

Happy Learning 🙂