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

# Load a CSV file

## Load a simple csv

This guide shows how to load a CSV file into a store thanks to a CSV source.\
For a description of what the CSV Source is, refer to the [CSV source](../csv_source).

### Goal

The goal is to load the first two columns of "trades.csv" file into the `Trades` store.

**File content**

```
id,amount,currency,trader,traderEntity,bank
1,12394,chf,E F,E3,BNP Paribas
2,13149,gbp,A B,E4,BNP Paribas
```

**Expected `Trades` content**

We want to load the first two columns into `Trades` store.

| id | amount |
| -- | ------ |
| 1  | 12394  |
| 2  | 13149  |

### Build a source

First step, in order to load a CSV file into a datastore, is to build a CSV source.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final ICSVSource<Path> csvSource = CsvSourceFactory.create();
```

A CSV source is a collection of CSV topics. CSV topics are references to a CSV file or a directory containing CSV files.\
They are associated to a parser configuration. Let's build this parser configuration.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final CSVParserConfiguration parserConfig = new CSVParserConfiguration(columnNames);
// Default separator is ',', you can customize this.
parserConfig.setSeparator(',');
// Skip the first header line if your file has a header.
parserConfig.setNumberSkippedLines(1);
// You can override the default charset
parserConfig.setCharset(StandardCharsets.UTF_8);
// Accept ignored supplementary columns
parserConfig.setAcceptOverflowingLines(true);
```

Then build a topic with the parser configuration.
This topic will load a single file in the `Trades` store.\
Because of this simple mapping the name of the store is used as a topic name.
This topic is registered into the source.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final String topicName = storeName;
// Will be close by source
final SingleFileCSVTopic csvTopic =
    new SingleFileCSVTopic(topicName, parserConfig, filePath, null);
csvSource.addTopic(csvTopic);
```

### Load into datastore

Second step is to create a channel and use the source to fetch the data into the Datastore.\
A channel is the link between a topic and a store.\
You can build a channel factory like this.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final IStoreMessageChannelFactory<IFileInfo<Path>, ILineReader> channelFactory =
    new CSVMessageChannelFactory<>(csvSource, datastore);
```

Finally, we use the source to process the channel.\
Source loads topic content using the channel and stream it into the Datastore.\
There is two ways of doing so.

Using the fetch utility :

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final Fetch<IFileInfo<Path>, ILineReader> fetch = new Fetch<>(channelFactory);
fetch.fetch(csvSource);
```

Or in a manual way :

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final IStoreMessageChannel<IFileInfo<Path>, ILineReader> channel =
    channelFactory.createChannel(STORE_NAME, STORE_NAME);
datastore.getTransactionManager().startTransaction();
csvSource.fetch(List.of(channel));
datastore.getTransactionManager().commitTransaction();
```

Be careful, `ICSVSource` is an `AutoCloseable` resource.\
Closing a source closes all the registered topics.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
csvSource.close();
```

## Load with a calculated column

### Goal

The goal is still to load the same file into the `Trades` store, but we want to compute a new column from the
amount column.

**Expected trade content**

| id | amount | negatedAmount |
| -- | ------ | ------------- |
| 1  | 12394  | -12394        |
| 2  | 13149  | -13149        |

### Load into the datastore

To add a new column which is based on existing ones we use an `IColumnCalculator`.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final AColumnCalculator<ILineReader> calculator =
    new AColumnCalculator<>(negatedAmountField) {
      @Override
      public Object compute(final IColumnCalculationContext<ILineReader> context) {
        final Long amountValue = (Long) context.getValue(AMOUNT_FIELD);
        return Math.negateExact(amountValue);
      }
    };
```

This calculator must be registered in the channel factory.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
channelFactory.setCalculatedColumns(STORE_NAME, List.of(calculator));
```

Then you can use your source to do the feeding as usual.

```java theme={"languages":{"custom":["/engine/python-sdk/6.2/languages/pycon.tmLanguage.json"]}}
final Fetch<IFileInfo<Path>, ILineReader> fetch = new Fetch<>(channelFactory);
fetch.fetch(csvSource);
```