# Pipeline variable resolver

### Functionality

We can create a new variable resolver metadata element of type `Pipeline Variable Resolver`. The options used are fairly simple:

* The pipeline filename to use: The file name of the pipeline to run to resolve a variable expression.
* Pipeline Run configuration name: this has to reference a run configuration of type: [Native Local](/data-shaper-1.21/knowing-the-data-shaper-designer/pipelines/pipeline-run-configurations/native-local-pipeline-engine.md).
* The name of the variable in the pipeline that will contain the expression to resolve
* The name of the output field to use to pick up the value of the fields.

This setup gives you a lot of flexibility. Maybe you have a configuration file per database, per system, …​ In that case you can set the variable to contain the type or name of the database, system, …​ to read a configuration file for. You can retrieve multiple values from these alternative configuration stores and send them to the output transform in a single row.

{% hint style="warning" %}
Only the first output row in the pipeline is considered.
{% endhint %}

The variable expression is (as always) in the following format:

`#{name:variable:field}`

* name: the name of the variable resolver metadata element to use
* variable: the variable value to set in the variable specified in the metadata (see above)
* field: the name of the field for which we want to retrieve a string in the output transform.

### Example

Suppose we have a number of databases we have configuration files for in separate properties files:

* db1.properties
* db2.properties
* db3.properties …​

These all contain the same 5 keys, with different values of-course:

```highlight
username=user1
password=pwd1
hostname=hostname1
port=port1
db=db1
```

We can then have a pipeline that reads and processes the appropriate file per type:

<figure><img src="/files/bU0ZlyIEaD0i51MjWIUd" alt=""><figcaption></figcaption></figure>

The Variable Resolver metadata would look like this:

<figure><img src="/files/kLVyDr5bMql3tBn5D4Qa" alt=""><figcaption></figcaption></figure>

Here are some examples of expressions and the results they give back:

* `#{conf:db1:username}` : user1
* `#{conf:db2:db}` : db2
* `#{conf:db3:port}` : port3

This gives you a lot of flexibility.

{% hint style="info" %}
In the case that you don’t specify any field to retrieve, the whole row will be encoded as a JSON value and given back.
{% endhint %}


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