> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hotglue.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Data Reading Functions

## Reader

A class for reading ETL files from the sync-output directory. This is the recommended way to read ETL files as it provides consistent error handling and metadata access.

### Basic Usage

```typescript theme={null}
import * as gs from '@hotglue/gluestick-ts';

const reader = new gs.Reader();
```

### Key Methods

***

## get(stream: string, options): DataFrame

Read a specific stream as a [Polars](https://pola-rs.github.io/nodejs-polars/) DataFrame

### Usage

```typescript theme={null}
// Basic reading
const df = reader.get("users");

// Type the dataframe according to the catalog
const df = reader.get("users", {
    catalogTypes: true
});
```

### Parameters

* `stream` (str): Name of stream to read
* `options` (obj)
  * `catalogTypes`: (boolean) - Use catalog for automatic type inference
  * Other options will be passed through to Polars when reading. See [ReadCSV](https://pola-rs.github.io/nodejs-polars/interfaces/ReadCsvOptions.html) and [ReadParquet](https://pola-rs.github.io/nodejs-polars/interfaces/ReadParquetOptions.html) options for more information

***

## getPk(stream: string): string\[]

Gets primary key(s) for a stream from catalog

### Usage

```typescript theme={null}
const primaryKeys = reader.getPk('users');
console.log(primaryKeys) 
// ["user_id", "region_id"]
```

### Parameters

* `stream` (string): Name of stream to get primary keys for

### Returns

* `string[]`: Array of primary key column names

***

## keys(): string\[]

Gets all available stream names from the input files.

### Usage

```typescript theme={null}
const availableStreams = reader.keys();
console.log(availableStreams);
// ["users", "orders", "products"]
```

### Returns

* `string[]`: Array of all available stream names

## Common Patterns

### Iterating through multiple streams

```typescript etl.ts theme={null}
import * as gs from '@hotglue/gluestick-ts';

// iterate through each stream in the input directory
const input = new gs.Reader();
const availableStreams = input.keys();

for (const key of availableStreams) {
    const inputDf = input.get(key, { catalogTypes: true });
}
```