> For the complete documentation index, see [llms.txt](https://docs.hackle.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.hackle.io/en/development-guide/android/user-identifier.md).

# User Identifier & Properties

{% hint style="info" %}
User Identifier Management

User Identifiers are used to uniquely identify users. For information about the meaning and importance of User Identifiers, and how to choose them, refer to the [Manage User Identifiers](/en/getting-started/user-identifier.md) documentation.
{% endhint %}

{% hint style="warning" %}
For functions that change user information (`setUser`, `setUserId`, `setDeviceId`, `updateUserProperties`, `resetUser`, and so on), we recommend using the variants that take a callback.

The callback is invoked after the changed user information has been applied to the SDK.
{% endhint %}

## User Identifier

### Default Identifiers Provided by Hackle

The Android SDK includes functionality to manage the device's identifier. Therefore, users can be automatically identified without separately providing a User Identifier.

You can query the identifiers managed by the SDK as follows.

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
// Get the device ID
val deviceId = hackleApp.deviceId

// Get the session ID
val sessionId = hackleApp.sessionId

// Get all user information
val user = hackleApp.user
```

{% endtab %}

{% tab title="Java" %}

```java
// Get the device ID
String deviceId = hackleApp.getDeviceId();

// Get the session ID
String sessionId = hackleApp.getSessionId();

// Get all user information
User user = hackleApp.getUser();
```

{% endtab %}
{% endtabs %}

#### Modify Device ID

You can inject a custom device ID instead of using the device ID provided by Hackle.

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
// Change the device ID
hackleApp.setDeviceId("CUSTOM_DEVICE_ID") {
    // Applied
}

// Using the builder pattern
val user = User.builder()
    .deviceId("CUSTOM_DEVICE_ID") // Device ID
    .build()

hackleApp.setUser(user) {
    // Applied
}
```

{% endtab %}

{% tab title="Java" %}

```java
// Change the device ID
hackleApp.setDeviceId("CUSTOM_DEVICE_ID", () -> {
    // Applied
});
```

{% endtab %}
{% endtabs %}

#### Set User Identifier (User ID)

You can set the identifier for a logged-in user.

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
// Add the logged-in user ID
hackleApp.setUserId("LOGIN_ID") {
    // Applied
}

// Using the builder pattern
val user = User.builder()
    .userId("LOGIN_ID") // User ID
    .build()

hackleApp.setUser(user) {
    // Applied
}
```

{% endtab %}

{% tab title="Java" %}

```java
// Add the logged-in user ID
hackleApp.setUserId("LOGIN_ID", () -> {
    // Applied
});
```

{% endtab %}
{% endtabs %}

### Additional Identifiers

You can add identifier types other than the default identifiers (deviceId, userId) as follows.

{% hint style="info" %}
Additional identifiers are not integrated with the [Hackle ID](/en/getting-started/user-identifier/hackle-id.md).
{% endhint %}

{% hint style="danger" %}
Calling `setUser` overwrites the current device's user information.

* If you are currently using userId A and call `setUser` without passing userId A, the userId changes from A to null.
* If you are currently using a custom deviceId and call `setUser` without passing the current deviceId, the custom deviceId reverts to the Hackle deviceId.
* If you use additional identifiers and do not pass them when calling `setUser`, the additional identifiers are reset.
* For properties, the cached properties on the device may be retained or reset in the following cases:
  * If the userId and deviceId are the same before and after `setUser`, cached properties are retained.
  * If the userId or deviceId changes before and after `setUser`, cached properties are deleted.
    {% endhint %}

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
import io.hackle.sdk.common.User

val user = User.builder()
    .userId("143")                   // User ID (Hackle ID can be used)
    .deviceId("ae2182e0")            // Device ID (Hackle ID can be used)
    .identifier("myCustomId", "42")  // Custom ID
    .build()

hackleApp.setUser(user) {
    // Applied
}
```

{% endtab %}

{% tab title="Java" %}

```java
import io.hackle.sdk.common.User

User user = User.builder()
    .userId("143")                   // User ID (Hackle ID can be used)
    .deviceId("ae2182e0")            // Device ID (Hackle ID can be used)
    .identifier("myCustomId", "42")  // Custom ID
    .build();

hackleApp.setUser(user, () -> {
    // Applied
});
```

{% endtab %}
{% endtabs %}

## User Property

The Hackle SDK supports adding user properties.

* Properties must be sent as key-value pairs (Property Key and Property Value).
* A maximum of 128 properties can be added.

<table><thead><tr><th width="133.04296875">Category</th><th width="127.60546875">Type</th><th>Constraints</th></tr></thead><tbody><tr><td>Property Key</td><td><code>string</code></td><td><ul><li>Character limit is 128 characters.</li><li>Case-insensitive.</li><li>For example, AGE and age are recognized as the same Property Key.</li></ul></td></tr><tr><td>Property Value</td><td><code>boolean</code>, <code>string</code>, <code>number</code>, <code>array</code></td><td><ul><li>For string type, the character limit is 1024 characters.</li><li>String type is case-sensitive.</li><li>For example, APPLE and apple are recognized as different Property Values.</li><li>For number type, up to 15 integer digits and up to 6 decimal places are supported.</li></ul></td></tr></tbody></table>

### Add User Property

You can add a user property simply by adding it with `set` on a `PropertyOperations` object and then calling `updateUserProperties`.

{% hint style="warning" %}
The `setUserProperty` function is deprecated as of Android SDK 4.0.0. Use `updateUserProperties` instead.
{% endhint %}

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
import io.hackle.sdk.common.PropertyOperations

// Set a property
val operations = PropertyOperations.builder()
    .set("gender", "female")
    .build()

hackleApp.updateUserProperties(operations) {
    // Applied
}
```

{% endtab %}

{% tab title="Java" %}

```java
import io.hackle.sdk.common.PropertyOperations;

// Set a property
PropertyOperations operations = PropertyOperations.builder()
    .set("gender", "female")
    .build();

hackleApp.updateUserProperties(operations, () -> {
    // Applied
});
```

{% endtab %}
{% endtabs %}

### Configure User Properties

You can add or remove user properties.

<table><thead><tr><th width="150">Supported Functions</th><th>Description</th></tr></thead><tbody><tr><td><code>set</code></td><td>Sets a User Property. If a Property Value already exists for the Property Key, it is overwritten.</td></tr><tr><td><code>setOnce</code></td><td><p>Sets a User Property value only once. If a property already exists for the Property Key, it is ignored.</p><p>For example, you can use this to set a user's registration date or initial sign-up location.</p></td></tr><tr><td><code>unset</code></td><td>Removes a User Property.</td></tr><tr><td><code>clearAll</code></td><td>Removes all User Properties.</td></tr></tbody></table>

Instantiate a `PropertyOperations` object with the user properties you want to configure. Then call `updateUserProperties` to update the user properties. You can configure multiple properties at once.

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
import io.hackle.sdk.common.PropertyOperations

// Set properties
val operations = PropertyOperations.builder()
    .set("age", 42)
    .set("grade", "GOLD")
    .setOnce("sign_up_date", "2020-07-03")
    .build()

hackleApp.updateUserProperties(operations) {
    // Applied
}

// Clear properties
val clearOperations = PropertyOperations.clearAll()

hackleApp.updateUserProperties(clearOperations) {
    // Applied
}
```

{% endtab %}

{% tab title="Java" %}

```java
import io.hackle.sdk.common.PropertyOperations;

// Set properties
PropertyOperations operations = PropertyOperations.builder()
    .set("age", 42)
    .set("grade", "GOLD")
    .setOnce("sign_up_date", "2020-07-03")
    .build();

hackleApp.updateUserProperties(operations, () -> {
    // Applied
});

// Clear properties
PropertyOperations clearOperations = PropertyOperations.clearAll();

hackleApp.updateUserProperties(clearOperations, () -> {
    // Applied
});
```

{% endtab %}
{% endtabs %}

## Reset User

You need to reset the previously configured information. When reset, all previously configured identifiers and properties are cleared.

{% hint style="danger" %}
Resetting the user also clears all user properties stored on the server. If you want to handle logout, use `hackleApp.setUserId(null)`.

Setting null to userId handles logout on the client side.
{% endhint %}

```kotlin
hackleApp.resetUser {
    // Applied
}
```


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