Package org.apache.calcite.rel

Interface RelWriter

All Known Implementing Classes:
RelDotWriter, RelJsonWriter, RelWriterImpl, RelXmlWriter
public interface RelWriter
Callback for an expression to dump itself to.

It is used for generating EXPLAIN PLAN output, and also for serializing a tree of relational expressions to JSON.

  • Method Summary

    Modifier and Type
    Method
    Description
    RelWriter
    done(RelNode node)
    Writes the completed explanation.
    void
    explain(RelNode rel, List<Pair<String,@Nullable Object>> valueList)
    Prints an explanation of a node, with a list of (term, value) pairs.
    SqlExplainLevel
    getDetailLevel()
    Returns detail level at which plan should be generated.
    default RelWriter
    input(String term, RelNode input)
    Adds an input to the explanation of the current node.
    RelWriter
    item(String term, @Nullable Object value)
    Adds an attribute to the explanation of the current node.
    default RelWriter
    itemIf(String term, @Nullable Object value, boolean condition)
    Adds an input to the explanation of the current node, if a condition holds.
    default boolean
    nest()
    Returns whether the writer prefers nested values.

  • Method Details

    • explain

      void explain(RelNode rel, List<Pair<String,@Nullable Object>> valueList)
      Prints an explanation of a node, with a list of (term, value) pairs.

      The term-value pairs are generally gathered by calling RelNode.explain(RelWriter). Each sub-class of RelNode calls input(String, org.apache.calcite.rel.RelNode) and item(String, Object) to declare term-value pairs.

      Parameters:
      rel - Relational expression
      valueList - List of term-value pairs

    • getDetailLevel

      SqlExplainLevel getDetailLevel()
      Returns detail level at which plan should be generated.

    • input

      default RelWriter input(String term, RelNode input)
      Adds an input to the explanation of the current node.
      Parameters:
      term - Term for input, e.g. "left" or "input #1".
      input - Input relational expression

    • item

      RelWriter item(String term, @Nullable Object value)
      Adds an attribute to the explanation of the current node.
      Parameters:
      term - Term for attribute, e.g. "joinType"
      value - Attribute value

    • itemIf

      default RelWriter itemIf(String term, @Nullable Object value, boolean condition)
      Adds an input to the explanation of the current node, if a condition holds.

    • done

      RelWriter done(RelNode node)
      Writes the completed explanation.

    • nest

      default boolean nest()
      Returns whether the writer prefers nested values. Traditional explain writers prefer flattened values.