# Custom Data Validation

In this guide, we will walk through a Data Application and a simple example implementation of an IoT use case. Complete code for this guide can be found in the [metagraph examples repo](https://github.com/Constellation-Labs/metagraph-examples) on Github. See the [Water and Energy Use](https://github.com/Constellation-Labs/metagraph-examples/tree/main/examples/DataApi-Water-And-Energy-Usage) example.

**Want more detail?**

Looking for additional detail on Data Application development? More information is available in [Data Application](/metagraph-development/metagraph-framework/data.md).

### Before You Start[​](https://docs.constellationnetwork.io/sdk/guides/custom-data#before-you-start) <a href="#before-you-start" id="before-you-start"></a>

In order to get started, install dependencies as described in the [Quick Start Guide](/metagraph-development/guides/quick-start.md). You will need at least the `global-l0`, `metagraph-l0`, and `metagraph-l1-data` containers enabled in your `euclid.json` file for this guide.

**Example euclid.json values**

```
  "version": "0.9.1",
  "tessellation_version": "2.2.0",
  "project_name": "custom-project",
  "framework": {
    "name": "currency",
    "modules": [
      "data"
    ],
    "version": "v2.2.0",
    "ref_type": "tag"
  },
  "layers": [
    "global-l0",
    "metagraph-l0",
    "currency-l1",
    "data-l1"
  ],
```

**Installing Templates with Hydra**

To initiate a metagraph using a template, we provide several options in our [GitHub repository](https://github.com/Constellation-Labs/metagraph-examples). Follow these steps to utilize a template:

1\.  List Available Templates: First, determine th\`e templates at your disposal by executing the command below:

```
./scripts/hydra install-template --list
```

2\.  Install a Template: After selecting a template, replace `:repo_name` with your chosen repository's name to install it. For instance:

```
./scripts/hydra install-template :repo_name
```

As a practical example, if you wish to install the `water-and-energy-usage` template, your command would look like this:

```
./scripts/hydra install-template water-and-energy-usage
```

This process will set up a metagraph based on the selected template.

Within your Euclid modules directory (source/project/water-and-energy-usage/modules) you will see three module directories: l0 (metagraph l0), l1 (currency l1), and data\_l1 (data l1). Each module has a Main.scala file that defines the application that will run at each corresponding layer.

```
- source
  - project
    - water-and-energy-usage
      - modules
        - l0
        - l1
        - data_1
        - shared_data
      - project
```

### Send Data[​](https://docs.constellationnetwork.io/sdk/guides/custom-data#send-data) <a href="#send-data" id="send-data"></a>

Edit the `send_data_transaction.js` script and fill in the `globalL0Url`, `metagraphL1DataUrl`, and `walletPrivateKey` variables. The private key can be generated with the `dag4.keystore.generatePrivateKey()` method if you don't already have one.

Once the variables are updated, save the file. You can now run `node send_data_transaction.js` to send data to the `/data` endpoint.

#### Check State Updates[​](https://docs.constellationnetwork.io/sdk/guides/custom-data#check-state-updates) <a href="#check-state-updates" id="check-state-updates"></a>

Using the custom endpoint created in the data\_l1 Main.scala `routes` method, we can check the metagraph state as updates are sent.

Using your browser, navigate to `<your L1 base url>/data-application/addresses` to see the complete state including all devices that have sent data. You can also check the state of an individual device using the `<your L1 base url>/data-application/addresses/:address` endpoint.

You should see a response like this:

```
{
    "DAG4bQGdnDJ5okVdsdtvJzBwQoPGjLNzN7HC1CBV": {
        "energy": {
            "usage": 7,
            "timestamp": 1689441998946
        },
        "water": {
            "usage": 7,
            "timestamp": 1689441998946
        }
    }
}
```

### Next Steps[​](https://docs.constellationnetwork.io/sdk/guides/custom-data#next-steps) <a href="#next-steps" id="next-steps"></a>

This brief guide demonstrates the ability to update and view on-chain state based on the Metagraph Framework's Data Application layer. Detailed information about the framework methods used can be found in the [example README file](https://github.com/Constellation-Labs/metagraph-examples/blob/main/examples/DataApi-Water-And-Energy-Usage/README.md) and in comments throughout the code. Also see additional break downs of the application lifecycle methods in the [Data API](/metagraph-development/metagraph-framework/data.md) section.


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