How do I check if a key exists in a JSON payload in DataWeave?

Append a question mark to the end of the field, like `payload.id?`. When the field has a value it returns `true`, and when the field doesn't exist it returns `false`.

How do I check for a key across multiple objects in an array?

You have two options shown in the post. The first, `payload.id?`, returns a single boolean that just tells you whether at least one object has the key, but not which one. The second, `payload map ((item, index) -> item.id?)`, iterates through each item so you can find out which specific object has the key present in it.

How do I check if a key is present inside a nested object?

First go to the parent object and then to the key, for example `payload.Address.zip?`, which returns `true` when the nested `zip` field is present.

What does the question mark operator return when checking a key?

It returns a boolean value: `true` when the field has a value, and `false` when the field doesn't exist.

How to check if a key is present in a JSON payload in DataWeave with these 3 examples

“In DataWeave, when a field in the input payload has a value and you append a question mark (?) at the end of the field, it will return true. On the other hand, if the field doesn’t exist, then it would return false.” Refer to the link below for more information:

https://blogs.mulesoft.com/dev-guides/how-to-tutorials/implement-logic-handling-in-dataweave/

Here are 3 examples where you can see how to check if a key in the input JSON payload is present or not.

1. Single Object

In this example, I have used a single JSON object to find if a key is present or not and the result will be a boolean value.

Input:

{
    "id":1,
    "company":"abc",
    "Address":"USA",
    "Phone":"123"
}

DataWeave Expression:

%dw 2.0
output application/json
---
payload.id?

Output:

true

2. Multiple Objects

For this example, we have multiple objects in an array and we are going to check if the key is present or not with different DataWeave Expressions which will give us different results.

In DataWeave Expression 1 the output returned is just a boolean value which helps to combine the result. But we won’t be able to know which object has id present in it. It just checks if there’s at least one value that matches the key and gives us a boolean value.

In DataWeave Expression 2 we will iterate through each item and then we can find out which item has id present in it. It gives complete information about a single object and the presence of the key in it.

Input:

[
    {
        "company":"abc",
        "Address":"USA",
        "Phone":"123"
    },
    {
        "id":1,
        "company":"def",
        "Address":"UK",
        "Phone":"345"
    }
]

DataWeave Expression 1:

%dw 2.0
output application/json
---
payload.id?

DataWeave Expression 2:

%dw 2.0
output application/json
---
payload map ((item, index) -> item.id?)

Output 1:

true

Output 2:

[
    false,
    true
]

3. Nested Objects

In this example, we have objects present in another object (nested objects). In this case, we will first go to the parent object and then to the key to find out whether it is present or not.

Input:

{
    "id":1,
    "company":"abc",
    "Address":{
        "street":"xyz",
        "zip":"080"
    },
    "Phone":"123"
}

DataWeave Expression:

%dw 2.0
output application/json
---
payload.Address.zip?

Output:

true

We have learned how we can check if the key is present or not within a different set of inputs and also observed different results obtained.

I hope this was useful to you.

1. Single Object

2. Multiple Objects

3. Nested Objects

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