/// <summary>
/// Writes table to this row group
/// </summary>
/// <param name="writer"></param>
/// <param name="table"></param>
public static void Write(this ParquetRowGroupWriter writer, Table table)
{
foreach (DataColumn dc in table.ExtractDataColumns())
{
writer.WriteColumn(dc);
}
}
/// <summary>
/// Serialises a collection of classes into a Parquet stream
/// </summary>
/// <typeparam name="T">Class type</typeparam>
/// <param name="objectInstances">Collection of classes</param>
/// <param name="destination">Destination stream</param>
/// <param name="schema">Optional schema to use. When not specified the class schema will be discovered and everything possible will be
/// written to the stream. If you want to write only a subset of class properties please specify the schema yourself.
/// </param>
/// <param name="compressionMethod"><see cref="CompressionMethod"/></param>
/// <param name="rowGroupSize"></param>
/// <param name="append"></param>
/// <returns></returns>
public static Schema Serialize <T>(IEnumerable <T> objectInstances, Stream destination,
Schema schema = null,
CompressionMethod compressionMethod = CompressionMethod.Snappy,
int rowGroupSize = 5000,
bool append = false)
where T : new()
{
if (objectInstances == null)
{
throw new ArgumentNullException(nameof(objectInstances));
}
if (destination == null)
{
throw new ArgumentNullException(nameof(destination));
}
if (!destination.CanWrite)
{
throw new ArgumentException("stream must be writeable", nameof(destination));
}
//if schema is not passed reflect it
if (schema == null)
{
schema = SchemaReflector.Reflect <T>();
}
using (var writer = new ParquetWriter(schema, destination, append: append))
{
writer.CompressionMethod = compressionMethod;
DataField[] dataFields = schema.GetDataFields();
foreach (IEnumerable <T> batch in objectInstances.Batch(rowGroupSize))
{
var bridge = new ClrBridge(typeof(T));
T[] batchArray = batch.ToArray();
DataColumn[] columns = dataFields
.Select(df => bridge.BuildColumn(df, batchArray, batchArray.Length))
.ToArray();
using (ParquetRowGroupWriter groupWriter = writer.CreateRowGroup())
{
foreach (DataColumn dataColumn in columns)
{
groupWriter.WriteColumn(dataColumn);
}
}
}
}
return(schema);
}
/// <summary>
/// Writes a file with a single row group
/// </summary>
public static void WriteSingleRowGroupParquetFile(this Stream stream, Schema schema, params DataColumn[] columns)
{
using (var writer = new ParquetWriter(schema, stream))
{
writer.CompressionMethod = CompressionMethod.None;
using (ParquetRowGroupWriter rgw = writer.CreateRowGroup())
{
foreach (DataColumn column in columns)
{
rgw.WriteColumn(column);
}
}
}
}
