# Dynamic Variable in MuleSoft

> On one of my assignments, I was presented with a rather peculiar demand: to write the records belonging to a unique identifier in a variable. The catch was, we do not know how many such unique identifiers are going to come in a particular batch. The flow will read an excel file and, based on the query string, we'll segregate the records -using a foreach component- and send an email with the final payload.

- **Author:** Soumyajit Sinha
- **Published:** Jun 8, 2021
- **Category:** Tutorials
- **Tags:** MuleSoft, DataWeave, Anypoint Studio
- **Source:** https://prostdev.com/post/dynamic-variable-in-mulesoft

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*GitHub repository with the Mule project can be found at the end of the post.*

On one of my assignments, I was presented with a rather peculiar demand. The demand was to write the records belonging to a unique identifier in a variable. Seems pretty easy, right?

But the catch was, we do not know how many such unique identifiers are going to come in a particular batch. So, to allocate a separate variable for segregating records belonging to a particular unique identifier where the number of such identifiers is unknown seemed to me like a task which needs some amount of research.

The immediate thought I got was, why not use a script which creates as many variables pertinent to the number of unique identifiers in a batch and then place all the records in the specific variable. In other words, I was thinking of creating a variable during the runtime.

As any developer would do, the first thing I did was to go to our own “stack-overflow”, i.e. MuleSoft documentation, to see if there is anything that is already available. Sadly, I could not find anything.

After hours of struggle and googling, I found a solution and it stuck to me that it might be helpful for other developers as well.

The idea was to create a POC to see whether the “idea” actually works or not. Basically, we will implement a flow which will:

- Will be listening to a HTTP call which will be equipped with a query parameter.
- Once the flow is summoned, it will read an excel file which has 3 features namely, “Name”, “Dept” & “Company”.
- Based on the query string, we will segregate the records and will send an email with the final payload.

## Let’s implement it in Anypoint Studio!

**1.** Create a new mule project in the studio.

**2.** Create a flow like this one:

![Mule flow: HTTP Listener, Read file, Logger, a For Each setting the dynamic variable, then Send email](../../assets/blog/dynamic-variable-in-mulesoft-1.png)

**3.** The HTTP request should be something like below:

![GET request to /dynamic-var with the query string Company=ImaginaryA annotated](../../assets/blog/dynamic-variable-in-mulesoft-2.png)

**4.** The file which we will be using looks like this:

![Excel sheet of Name, Dept, and Company rows across four imaginary companies](../../assets/blog/dynamic-variable-in-mulesoft-3.png)

Here, there are 4 companies namely, ImaginaryA, ImaginaryB, ImaginaryC & ImaginaryD. There are 2 departments namely, Dev & Support.

Let’s dive deeper into the DataWeave scripts and the for-each that we have used.

## Prerequisites

Well you may ask this question: How to read an excel file (or as a matter of fact, any file) from your local system?

Here you go!

**1.** First you need to use a “Read” component from the “File” palette and give the location of the file. You can get the “path” of a file by doing the following:

Right click on the file and click on the “Security” tab.

![Windows file Properties dialog for the .xlsx test document, Security tab highlighted](../../assets/blog/dynamic-variable-in-mulesoft-4.png)

You can see “Object Name” on the top which depicts the location/path of the file that you are willing to use. Copy that string and keep it handy.

**2.** Come back inside Anypoint Studio and click on the “Read” component.

First Configuration

![Read component config with File Path set to p('fileLocation') and no errors](../../assets/blog/dynamic-variable-in-mulesoft-5.png)

While copying the “path”, you will get something like C:\Users\Documents\Test Files\<<File Name>>. Mule does not understand “\”. Make sure to replace “\” with “/”.

So the final address you should be using for the “File Path” in the above configuration should be something like C:/Users/Documents/Test Files/<<File Name>>.

Second Configuration

You need to add the MIME Type. Since in this case we are dealing with an excel file, we will be keeping the MIME Type as application/xlsx.

![Read component MIME Type tab set to application/xlsx for the Excel file](../../assets/blog/dynamic-variable-in-mulesoft-6.png)

**3.** Once this is done, we need to specify which sheet we are trying to read. A simple DataWeave script can help!

![Set Payload component with a DataWeave script reading payload."Sheet1"](../../assets/blog/dynamic-variable-in-mulesoft-7.png)

By writing payload.“Sheet1”, we are instructing it to read the data which is there in the Sheet1.

Now that you know how to read an excel file, we are good to go ahead. Let's explore now!

## Let's head back to our studio

**1.** Once the file is read, we have logged the payload to see what is being fed to the mule flow (Refer to the prerequisites to learn about reading a file).

![Logged payload showing each record's Name, Dept, and Company as JSON objects](../../assets/blog/dynamic-variable-in-mulesoft-8.png)

**2.** We can see that the payload is being read like above. So, to intercept the entire payload as individual chunks, we have used a for-each which divides the payload uniformly.

**3.** On the onset of the flow, we have captured the queryString. A query string contains the total string which we have passed in the URL.

![GET request URL with the Company=ImaginaryA portion labeled as the query string](../../assets/blog/dynamic-variable-in-mulesoft-9.png)

**4.** Once we reach inside the payload, we split the query string by the separator “=”.

![Set Variable named segBy with value vars.queryString splitBy "="](../../assets/blog/dynamic-variable-in-mulesoft-10.png)

We can see **Company** as **segBy[0]** and **ImaginaryA** as **segBy[1]** (please check the above point for getting the references).

**5.** Once that is done, we will write the DataWeave script to implement the dynamic variable concept.

![set-variable XML using a dynamicVar to build a variable name from segBy[0] at runtime](../../assets/blog/dynamic-variable-in-mulesoft-11.png)

The name of the variable is kept in accordance with the feature, which we have mentioned in the query string, by which we want to segregate our records. In this case we want that feature to be Company.

Here in the 3rd line, we have written dynamicVar = payload[vars.segBy[0] as String] as String

- We have created a local variable named dynamicVar which will create a placeholder as per the number of companies in the payload.
- This will be dynamic in nature, which means that the number of variables to be created will be decided during the runtime.

The script that follows it simply checks if the company named variable is available or not.

- If available, it pushes the records into that already available variable.
- If not available, it creates the company named variable and then inserts the records.

**6.** Once that is done, we will send an email to confirm whether our code has worked or not. In order to summon the variable, we will use the following script.

![Email Body config reading the dynamic variable via vars[vars.segBy[1]] as plain text](../../assets/blog/dynamic-variable-in-mulesoft-12.png)

In our case since we have 4 companies in our payload, 4 variables will be created. Now, if you remember the query string, we want the records belonging to the company **ImaginaryA.** The command **segBy[1]** will return the value **ImaginaryA** (please check step 4).

Hence, by the command we are trying to access the variable created for **ImaginaryA**.

**7.** Once the process completes, as per the POC we should receive a mail which should look something like this:

![Received email listing only the ImaginaryA employee records in CSV format](../../assets/blog/dynamic-variable-in-mulesoft-13.png)

So, finally we have a solution which can address our issue.

## GitHub repository

[ProstDev GitHub - Dynamic Variable Mule](https://github.com/ProstDev/dynamic-variable-mule)

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## FAQs

### What problem does the dynamic variable approach solve?

The assignment was to write the records belonging to a unique identifier into a variable when you do not know how many such unique identifiers will arrive in a particular batch. Since you cannot allocate a separate variable ahead of time for an unknown number of identifiers, the solution creates variables during runtime, building as many variables as there are unique identifiers in the batch and placing each record in its specific variable.

### How do I read an Excel file from my local system in the flow?

Use a `Read` component from the File palette and give it the location of the file, then add the MIME Type, which for an Excel file is `application/xlsx`. To get the path on Windows, right-click the file, open the Security tab, and copy the Object Name shown at the top. Because Mule does not understand the backslash, replace every `\` with `/` so a path like `C:\Users\Documents\Test Files\<<File Name>>` becomes `C:/Users/Documents/Test Files/<<File Name>>`.

### How does the flow split the query string to drive the dynamic variable?

On the onset of the flow the queryString is captured from the URL, then inside the payload it is split by the separator `=` using a Set Variable named `segBy` with the value `vars.queryString splitBy "="`. With a query string of Company=ImaginaryA, `segBy[0]` becomes Company (the feature to segregate by) and `segBy[1]` becomes ImaginaryA (the value to retrieve).

### How is the variable name created at runtime?

A local variable `dynamicVar` is built from the feature in the query string, written as `dynamicVar = payload[vars.segBy[0] as String] as String`, which creates a placeholder per company in the payload. The script then checks whether the company-named variable already exists; if it does, it pushes the records into that existing variable, and if it does not, it creates the company-named variable and then inserts the records.

### How do I retrieve the records for a specific company at the end?

The email body summons the variable with `vars[vars.segBy[1]]`. Since the example payload has four companies, four variables are created, and because `segBy[1]` returns ImaginaryA from the query string, that command accesses the variable created for ImaginaryA, so the received email lists only the ImaginaryA records.

### Where can I find the Mule project for this post?

The GitHub repository with the Mule project is linked at the end of the post at https://github.com/ProstDev/dynamic-variable-mule.