org.apache.calcite.rel

Interface RelWriter

All Known Implementing Classes:

AbstractRelNode.RelDigestWriter, 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 and Description
RelWriter	done(RelNode node) Writes the completed explanation.
void	explain(RelNode rel, java.util.List<Pair<java.lang.String,java.lang.Object>> valueList) Prints an explanation of a node, with a list of (term, value) pairs.
SqlExplainLevel	getDetailLevel()
default RelWriter	input(java.lang.String term, RelNode input) Adds an input to the explanation of the current node.
RelWriter	item(java.lang.String term, java.lang.Object value) Adds an attribute to the explanation of the current node.
default RelWriter	itemIf(java.lang.String term, java.lang.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 Detail

explain

void explain(RelNode rel,
             java.util.List<Pair<java.lang.String,java.lang.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(java.lang.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(java.lang.String term,
               java.lang.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(java.lang.String term,
                         java.lang.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.