Joseph Doherty
f5468d019f
Add MapOrdinal method to the IDataTransformer interface and provide a default implementation in DataTransformerBase. This enables transformers to report the mapping between transformed ordinals and source ordinals, supporting use cases like computed columns which return -1 to indicate no source ordinal. - Add MapOrdinal(int, IDataReader) to IDataTransformer interface - Add virtual MapOrdinal implementation in DataTransformerBase - Add DataTransformerBaseTests with test for default behavior
75 lines
2.8 KiB
C#
75 lines
2.8 KiB
C#
using System.Data;
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using JdeScoping.DataSync.Etl.Contracts;
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namespace JdeScoping.DataSync.Etl.Transformers;
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/// <summary>
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/// Base class for data transformers that modify data during the ETL process.
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/// Derived classes can override specific methods to customize transformation behavior.
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/// </summary>
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public abstract class DataTransformerBase : IDataTransformer
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{
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/// <inheritdoc />
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public abstract string TransformerName { get; }
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/// <inheritdoc />
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public IDataReader Transform(IDataReader source)
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{
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ArgumentNullException.ThrowIfNull(source);
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OnInitialize(source);
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return new TransformingDataReader(source, this);
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}
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/// <summary>
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/// Called when the transformer is initialized with a source reader.
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/// Override to perform initialization logic.
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/// </summary>
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/// <param name="source">The source data reader.</param>
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protected virtual void OnInitialize(IDataReader source) { }
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/// <summary>
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/// Gets the field count from the source reader.
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/// Override to add or remove fields.
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/// </summary>
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public virtual int GetFieldCount(IDataReader source) => source.FieldCount;
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/// <summary>
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/// Gets the name of a field at the specified ordinal.
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/// Override to rename fields.
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/// </summary>
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public virtual string GetName(int ordinal, IDataReader source) => source.GetName(ordinal);
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/// <summary>
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/// Gets the type of a field at the specified ordinal.
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/// Override to change field types.
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/// </summary>
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public virtual Type GetFieldType(int ordinal, IDataReader source) => source.GetFieldType(ordinal);
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/// <summary>
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/// Gets the value of a field at the specified ordinal.
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/// Override to transform values.
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/// </summary>
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public virtual object GetValue(int ordinal, IDataReader source) => source.GetValue(ordinal);
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/// <summary>
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/// Gets the ordinal of a field by name.
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/// Override to support renamed fields.
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/// </summary>
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public virtual int GetOrdinal(string name, IDataReader source) => source.GetOrdinal(name);
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/// <summary>
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/// Checks if a field value is DBNull.
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/// Override to handle null transformations.
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/// </summary>
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public virtual bool IsDBNull(int ordinal, IDataReader source) => source.IsDBNull(ordinal);
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/// <summary>
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/// Maps a transformed ordinal to the source ordinal.
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/// Override to support column reordering or computed columns.
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/// </summary>
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/// <param name="transformedOrdinal">The ordinal in the transformed output.</param>
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/// <param name="source">The source data reader.</param>
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/// <returns>The corresponding source ordinal, or -1 for computed columns.</returns>
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public virtual int MapOrdinal(int transformedOrdinal, IDataReader source) => transformedOrdinal;
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}
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