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Parquet

The parquet connector pack allow you to read or write data from or into parquet files.

Parquet source

The ETLBox.Parquet   package include the ParquetSource and ParquetDestination classes.

The csv connector package is based on the Parquet .NET library created by Elastacloud   . The parquet source let you read data from a parquet file.

Parquet is an open source file format, which stores data in a columnar storage format (in opposite to e.g. csv files, where data is stored row based.) While storing data in a column based manner has many advantages regarding efficiency and storage size, parquet data needs to be read as rows from the files in order to work with ETLBox. The ParquetSource will read all data from the parquet file as rows - starting with the first row until the end of the file (or a defined limit). Internally, the columnar format is translated into rows while reading data.

Note

All streaming connectors share a set of common properties. For example, instead of reading or writing from/into a file you can set ResourceType to ResourceType.Http or ResourceType.AzureBlob in order to read or write into a web endpoint or an Azure blob. See shared functionalities for a list of all shared properties between all streaming connectors.

Example

Let’s assume we have a parquet file “Demo.parquet” that has 2 columns, named Col1 and Col2. Here is a simple example to read data all data from this parquet file and write it into an in-memory list.

public class MyRow
{
    public int Col1 { get; set; }        
    public string Col2 { get; set; }            
}

ParquetSource<MyRow> source = new ParquetSource<MyRow>();
source.Uri = "Demo.parquet";
MemoryDestination<MyRow> dest = new MemoryDestination<MyRow>();

source.LinkTo(dest);
Network.Execute(source);
//All rows available in dest.Data

Mapping different column names

If you want to map the defined column names in the parquet file to a property with a different name, you can use the ParquetColumn attribute. The following object definition would work with the same file as in the previous example, but would map Col1 from the file with the property Id and Col2 with the property Value.

public class MyRow
{
    [ParquetColumn(ColumnName ="Col1")]
    public int Id { get; set; }

    [ParquetColumn(ColumnName = "Col2")]
    public string Value { get; set; }            
}

Using dynamic objects

If you don’t want to use a strongly typed object, you can also use the dynamic version which uses the ExpandoObject to create objects on the fly.

ParquetSource source = new ParquetSource();
source.Uri = "Demo.parquet";
MemoryDestination dest = new MemoryDestination();
            
source.LinkTo(dest);
Network.Execute(source);
//All rows available in dest.Data, stored in a list of ExpandoObjects

Attributes and dynamic objects

You can also use the ParquetColumn attribute when working with dynamic objects. This code would give you the same mapping as in the example before with the strongly typed object:

ParquetSource<MyRow> source = new ParquetSource<MyRow>();
source.Uri = "Demo.parquet";
source.ParquetColumns = new[] {
    new ParquetColumn() { PropertyName = "Id", ColumnName = "Col1"},
    new ParquetColumn() { PropertyName = "Value", ColumnName = "Col2"},
};
MemoryDestination dest = new MemoryDestination<MyRow>();
source.LinkTo(dest);
Network.Execute(source);

Parquet Destination

ETLBox makes writing into a parquet file very simple. The ParquetDestinatinon will convert the incoming rows from your source into a columnar format and then store the data into the file. Internally, the parquet file specifies row groups for a set of column - by default, ETLBox will create a new RowGroup foreach batch of 1000 records. This value can be changed by setting the BatchSize property.

Example

public class MyRow
{
    public int Col1 { get; set; }
    public string Col2 { get; set; }            
}

var source = new MemorySource<MyRow>();            
source.DataAsList.Add(new MyRow() { Col1 = 1, Col2 = "Test1" });
source.DataAsList.Add(new MyRow() { Col1 = 2, Col2 = null });
source.DataAsList.Add(new MyRow() { Col1 = 3, Col2 = "Test3"});

var dest = new ParquetDestination<MyRow>("./SimpleWithObject.parquet");
source.LinkTo(dest);

Network.Execute(source);

Mapping different column names

Like in the ParquetSource, the ParquetColumn attribute can be used to store the columns with a different name in the file. For example, the following code snipped would store the data from the properties Id and Value in the file with the column names Col1 and Col2. You can set a WriteOrder in the attribute if you want to specify a particular order when storing the columns. In this example the column Col2 would be the first column in the parquet file.

public class MyOrderedRow
{    
    [ParquetColumn(ColumnName = "Col1", WriteOrder =2)]
    public int Id { get; set; }
    public string Clutter { get; set; }
    [ParquetColumn(ColumnName = "Col2", WriteOrder = 1)]
    public string Value { get; set; }
}

var source = new MemorySource<MyOrderedRow>();
source.DataAsList.Add(new MyOrderedRow() { Id = 1, Value = "Test1" });
source.DataAsList.Add(new MyOrderedRow() { Id = 2, Value = null });
source.DataAsList.Add(new MyOrderedRow() { Id = 3, Value = "Test3" });

var dest = new ParquetDestination<MyOrderedRow>("./AttributesWithOrder.parquet");
source.LinkTo(dest);

Network.Execute(source);

Using dynamic objects

Of course you can also make use of the dynamic ExpandoObject when storing data with the ParquetDestination.

var source = new MemorySource();
dynamic r1 = new ExpandoObject();
r1.Col1 = 1; r1.Col2 = "Test1";
source.DataAsList.Add(r1);
dynamic r2 = new ExpandoObject();
r2.Col1 = 2; r2.Col2 = null;
source.DataAsList.Add(r2);

var dest = new ParquetDestination("./SimpleWithDynamic.parquet");
source.LinkTo(dest);

Network.Execute(source);

Manual attributes for dynamic objects

The attribute columns can also be assigned manually (either for dynamic or strongly typed objects)

var source = new MemorySource();
dynamic r1 = new ExpandoObject();
r1.Id = 1; r1.Value= "Test1";
source.DataAsList.Add(r1);

var dest = new ParquetDestination("./ManualAttributesOnDynamicWithOrder.parquet");
dest.ParquetColumns = new[] {
    new ParquetColumn() { PropertyName = "Id", ColumnName = "Col1", WriteOrder = 2},
    new ParquetColumn() { PropertyName = "Value", ColumnName = "Col2"}
};
source.LinkTo(dest);
Network.Execute(source);
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