# Create a Sync from Clickhouse to Batch Profile Attributes

### Before you start

To create a ClickHouse → Batch sync, you'll need:

* Access to the **Batch dashboard**
* A **ClickHouse table or view** containing one row per profile
* Your **ClickHouse credentials** (Host, Port, Database, Username, Password)
* A table (or view) that follows the **Cloud Sync input format** (see below)

***

### 1) Prepare your ClickHouse table or view

Cloud Sync expects your ClickHouse source (table or view) to include:

1. A **profile identifier** (to know which profile to update)
2. A **cursor field** (to know what changed since the last run)
3. Any number of **attribute columns** (sent to Batch as profile attributes)

***

#### 1.1 One row per profile

Your source must contain **one row per profile**.\
Each row is interpreted as an update to a single Batch profile.

***

#### 1.2 Required columns

Your table (or view) must include:

| Column            | Required | Description                      |
| ----------------- | :------: | -------------------------------- |
| `custom_id`       |     ✅    | The profile identifier in Batch  |
| `last_updated_at` |     ✅    | Cursor used for incremental sync |

{% hint style="warning" %}
`last_updated_at` must be updated **every time any synced attribute changes**, otherwise updates may not be picked up by the next run.
{% endhint %}

***

#### 1.3 Attribute naming rules (ClickHouse-compatible)

Cloud Sync reads ClickHouse columns and converts them into Batch profile attributes.

ClickHouse column names do not support characters like `$`, `(`, or `)`. Cloud Sync relies on **prefixes** in column names to represent typed or native fields.

**Supported prefixes**

| Prefix    | Meaning                                   | Example                |
| --------- | ----------------------------------------- | ---------------------- |
| `date__`  | Date attribute                            | `date__birthday`       |
| `url__`   | URL attribute                             | `url__avatar`          |
| `batch__` | Native profile fields (instead of `$...`) | `batch__email_address` |

***

#### 1.4 Handling arrays

Array attributes must be passed as a **`String` column** containing a stringified JSON array. Native ClickHouse `Array()` types are not supported.

```sql
'["value1","value2","value3"]'
```

Example:

```sql
SELECT
  user_id                          AS custom_id,
  updated_at                       AS last_updated_at,
  '["art","design"]'               AS interests  -- String, not Array(String)
FROM raw.users;
```

***

#### 1.5 Example schema (e-commerce)

```sql
CREATE TABLE customer_data.batch_profiles (
    custom_id            String,
    last_updated_at      DateTime64(3, 'UTC'),

    -- Native profile fields
    batch__email_address String,

    -- Standard attributes
    plan                 String,
    country              String,
    lifetime_value       Float64,
    is_vip               UInt8,

    -- Array attribute (stringified, not Array(String))
    interests            String,   -- e.g. '["art","design"]'

    -- Typed attributes
    url__avatar          String,
    date__birthday       String,
    date__last_purchase  String
) ENGINE = MergeTree()
ORDER BY (custom_id);
```

**How this maps in Batch:**

* `custom_id` identifies the profile
* `batch__email_address` updates the profile's native email field
* `plan`, `country`, `lifetime_value`, `is_vip` become standard attributes
* `interests` is interpreted as an array attribute (must be a stringified JSON array)
* `url__avatar` is interpreted as a URL attribute
* `date__birthday` and `date__last_purchase` are interpreted as date attributes

***

#### 1.6 Using a View

If your raw table doesn't match the expected naming or format, create a **ClickHouse View** that converts your schema into the correct conventions.

```sql
CREATE OR REPLACE VIEW customer_data.batch_profiles_view AS
SELECT
  toString(u.user_id)                              AS custom_id,
  greatest(u.updated_at, o.last_order_updated_at)  AS last_updated_at,

  u.email                                          AS batch__email_address,
  u.country,
  u.plan,

  u.avatar_url                                     AS url__avatar,
  formatDateTime(u.birth_date, '%Y-%m-%d')         AS date__birthday,

  o.last_order_date                                AS date__last_purchase,
  o.total_spent                                    AS lifetime_value,
  u.is_vip,

  -- Stringify arrays before passing to Cloud Sync
  toJSONString(u.interests)                        AS interests
FROM raw.users u
LEFT JOIN raw.user_orders_summary o
  ON u.user_id = o.user_id;
```

This approach lets you:

* rename fields with the correct prefixes (`batch__`, `date__`, `url__`)
* compute a reliable `last_updated_at`
* stringify array columns correctly
* ensure you always expose **one row per profile**

***

#### 1.7 Handling nulls

If a column value is `NULL`, Batch interprets it as **attribute removal** for that profile.

If you don't want an attribute removed:

* ensure your view returns a non-null value, or
* exclude the column from the sync entirely.

***

#### 1.8 Attributes limits and constraints

All attributes sent through Cloud Sync must respect the same limits and constraints as the Batch Profile API. See Profile API documentation, [the attributes object](https://doc.batch.com/getting-started/features/customer-engagement-platform).

***

### 2) Create the Sync in the Batch dashboard

Cloud Sync is configured from the dashboard via a dedicated **Sync module**.

1. Open the **Batch dashboard**
2. Go to **Data → Cloud Sync**
3. Click **Create Sync**
4. Select **ClickHouse** as the source

***

#### 2.1 Configure your ClickHouse connection

Enter the following fields:

| Field    | Description                                                         |
| -------- | ------------------------------------------------------------------- |
| Host     | Your ClickHouse server hostname (e.g. `your-host.example.com`)      |
| Port     | ClickHouse HTTP(S) port — defaults to `8123`                        |
| Database | The database containing your source table/view (default: `default`) |
| Username | Your ClickHouse username                                            |
| Password | Your ClickHouse password                                            |
| SSL      | Toggle on to use a secure connection (recommended for production)   |
| Table    | The table or view name                                              |

Batch validates the connection before continuing.

***

#### 2.2 Configure profile mapping

Cloud Sync applies a simple mapping model:

* `custom_id` → identifies which Batch profile to update
* all other columns → mapped to profile attributes
* `last_updated_at` → used only for incremental sync logic

***

### 3) How incremental sync works

Cloud Sync uses **incremental processing**, which means it does not re-import your full dataset at every run. Instead, it fetches only the rows that changed since the last successful sync.

***

#### 3.1 The `last_updated_at` cursor

Batch stores the last successful cursor value internally.

At each run, Batch fetches only rows where:

* `last_updated_at` is greater than the last stored cursor

This makes sync runs faster, more scalable, and more cost-efficient.

***

#### 3.2 Inserts, updates, and deletes

Incremental syncs naturally capture:

* ✅ inserts
* ✅ updates

They do **not** automatically capture:

* ❌ deletes

If you need deletions reflected in Batch, rely on a different pipeline or implement soft deletes by setting all attributes to null in the ClickHouse view when a profile is deleted.

***

#### 3.3 Best practices for reliable incremental syncs

To avoid missing changes:

* Ensure `last_updated_at` updates **every time a synced column changes**
* Avoid timestamps that only reflect partial updates
* Use a View if you need computed fields or type conversions
* Use `ReplacingMergeTree` and order by `last_updated_at` for large tables

***

### 4) Test and enable your Sync

Before enabling the schedule:

1. Run a **test sync**
2. Verify:
   * Profiles are created or updated correctly
   * `batch__`, `date__`, and `url__` fields are interpreted correctly
   * Array attributes are correctly stringified (e.g. `["art","design"]`)
   * Null values behave as expected (null → attribute removal)

Once enabled, Batch automatically handles batching and retries.


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