Simple Plugin

The tutorial explains how to create custom plugin based on IRowsInput interface.

1. Add any new input source based on IRowsInput interface.

   /// <summary>
   /// Example simple rows input plugin.
   /// </summary>
   public class SamplePluginRowsInput : IRowsInput
   {
       private const long MaxValue = 9;
   
       [Description("Sample input.")]
       [FunctionSignature("plugin(start: integer = 0): object<IRowsInput>")]
       public static VariantValue SamplePlugin(IExecutionThread thread)
       {
           var startValue = thread.Stack.Pop().AsInteger;
           var rowsSource = new SamplePluginRowsInput(startValue ?? 0);
           return VariantValue.CreateFromObject(rowsSource);
       }
   
       private long _currentState;
   
       /// <inheritdoc />
       public Column[] Columns { get; } =
       [
           new("id", DataType.Integer, "Key.")
       ];
   
       /// <inheritdoc />
       public string[] UniqueKey { get; } = [];
   
       /// <inheritdoc />
       public QueryContext QueryContext
       {
           get => NullQueryContext.Instance;
           set => Trace.WriteLine($"Set {nameof(QueryContext)}");
       }
   
       public SamplePluginRowsInput(long initialValue)
       {
           _currentState = initialValue;
       }
   
       /// <inheritdoc />
       public Task OpenAsync(CancellationToken cancellationToken = default)
       {
           Trace.WriteLine(nameof(OpenAsync));
           return Task.CompletedTask;
       }
   
       /// <inheritdoc />
       public Task CloseAsync(CancellationToken cancellationToken = default)
       {
           Trace.WriteLine(nameof(CloseAsync));
           return Task.CompletedTask;
       }
   
       /// <inheritdoc />
       public ErrorCode ReadValue(int columnIndex, out VariantValue value)
       {
           Trace.WriteLine(nameof(ReadValue));
           if (columnIndex == 0)
           {
               value = new VariantValue(_currentState);
               return ErrorCode.OK;
           }
   
           value = default;
           return ErrorCode.InvalidColumnIndex;
       }
   
       /// <inheritdoc />
       public ValueTask<bool> ReadNextAsync(CancellationToken cancellationToken = default)
       {
           Trace.WriteLine(nameof(ReadNextAsync));
           if (_currentState >= MaxValue)
           {
               return ValueTask.FromResult(false);
           }
           _currentState++;
           return ValueTask.FromResult(true);
       }
   
       /// <inheritdoc />
       public Task ResetAsync(CancellationToken cancellationToken = default)
       {
           Trace.WriteLine(nameof(ResetAsync));
           _currentState = 0;
           return Task.CompletedTask;
       }
   
       /// <inheritdoc />
       public void Explain(IndentedStringBuilder stringBuilder)
       {
           stringBuilder.AppendLine("Sample");
       }
   
       /// <inheritdoc />
       public IReadOnlyList<KeyColumn> GetKeyColumns() => [];
   
       /// <inheritdoc />
       public void SetKeyColumnValue(int columnIndex, VariantValue value, VariantValue.Operation operation)
       {
       }
   
       /// <inheritdoc />
       public void UnsetKeyColumnValue(int columnIndex, VariantValue.Operation operation)
       {
       }
   }

2. Add function definition for the new source. For example:

   [Description("Sample input.")]
   [FunctionSignature("plugin(start: integer = 0): object<IRowsInput>")]
   public static VariantValue SamplePlugin(IExecutionThread thread)
   {
       var startValue = thread.Stack.Pop().AsInteger;
       var rowsSource = new SamplePluginRowsInput(startValue ?? 0);
       return VariantValue.CreateFromObject(rowsSource);
   }

3. Publish the plugin:

   dotnet publish ./SimplePlugin/

4. Run QueryCat with the new plugin.

   qcat "select * from plugin()" --plugin-dirs /mnt/data/work/SimplePlugin/SimplePlugin/bin/Debug/net10.0/publish/

   | id    |
   | ----- |
   | 1     |
   | 2     |
   | 3     |
   | 4     |
   | 5     |
   | 6     |
   | 7     |
   | 8     |
   | 9     |