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/*
* Copyright (c) "Neo4j"
* Neo4j Sweden AB [https://neo4j.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
* The result is comprised of a number of rows, potentially computed lazily, with this result object being an iterator
* over those rows. Each row is represented as a {@link Map}<{@link String}, {@link Object}>, the
* keys in this map are the names of the columns in the row, as specified by the {@code return} clause of the query,
* and the values of the map is the corresponding computed value of the expression in the {@code return} clause. Each
* row will thus have the same set of keys, and these keys can be retrieved using the
* {@linkplain #columns() columns-method}.
*
* To ensure that any resource, including transactions bound to the query, are properly freed, the result must either
* be fully exhausted, by means of the {@linkplain java.util.Iterator iterator protocol}, or the result has to be
* explicitly closed, by invoking the {@linkplain #close() close-method}.
*
* Idiomatic use of the Result object would look like this:
*
* try ( Result result = graphDatabase.execute( query, parameters ) )
* {
* while ( result.hasNext() )
* {
* Map<String, Object> row = result.next();
* for ( String key : result.columns() )
* {
* System.out.printf( "%s = %s%n", key, row.get( key ) );
* }
* }
* }
*
* If the result consists of only a single column, or if only one of the columns is of interest, a projection can be
* extracted using {@link #columnAs(String)}. This produces a new iterator over the values of the named column. It
* should be noted that this iterator consumes the rows of the result in the same way as invoking {@link #next()} on
* this object would, and that the {@link #close() close-method} on either iterator has the same effect. It is thus
* safe to either close the projected column iterator, or this iterator, or both if all rows have not been consumed.
*
* In addition to the {@link #next() iteration methods} on this interface, {@link #close()}, and the
* {@link #columnAs(String) column projection method}, there are two methods for getting a string representation of the
* result that also consumes the entire result if invoked. {@link #resultAsString()} returns a single string
* representation of all (remaining) rows in the result, and {@link #writeAsStringTo(PrintWriter)} does the same, but
* streams the result to the provided {@link PrintWriter} instead, without allocating large string objects.
*
* The methods that do not consume any rows from the result, or in other ways alter the state of the result are safe to
* invoke at any time, even after the result has been {@linkplain #close() closed} or fully exhausted. These methods
* are:
*
* - {@link #columns()}
* - {@link #getQueryStatistics()}
* - {@link #getQueryExecutionType()}
* - {@link #getExecutionPlanDescription()}
*
*
* Not all queries produce an actual result, and some queries that do might yield an empty result set. In order to
* distinguish between these cases the {@link QueryExecutionType} {@linkplain #getQueryExecutionType() of this result}
* can be queried.
*/
@PublicApi
public interface Result extends ResourceIterator> {
/**
* Indicates what kind of query execution produced this result.
*
* @return an object that indicates what kind of query was executed to produce this result.
*/
QueryExecutionType getQueryExecutionType();
/**
* The exact names used to represent each column in the result set.
*
* @return List of the column names.
*/
List columns();
/**
* Returns an iterator with the result objects from a single column of the result set. This method is best used for
* single column results.
*
* To ensure that any resources, including transactions bound to it, are properly closed, the iterator must
* either be fully exhausted, or the {@link org.neo4j.graphdb.ResourceIterator#close() close()} method must be
* called.
*
* As an example, if we are only interested in a column {@code n} that contains node values, we can extract it like
* this:
*
* try ( ResourceIterator<Node> nodes = result.columnAs( "n" ) )
* {
* while ( nodes.hasNext() )
* {
* Node node = nodes.next();
* // Do some work with the 'node' instance.
* }
* }
*
*
* @param name exact name of the column, as it appeared in the original query
* @param desired type cast for the result objects
* @return an iterator of the result objects, possibly empty
* @throws ClassCastException when the result object can not be cast to the requested type
* @throws org.neo4j.graphdb.NotFoundException when the column name does not appear in the original query
*/
ResourceIterator columnAs(String name);
/**
* Denotes there being more rows available in this result. These rows must either be consumed, by invoking
* {@link #next()}, or the result has to be {@link #close() closed}.
*
* @return {@code true} if there is more rows available in this result, {@code false} otherwise.
*/
@Override
boolean hasNext();
/**
* Returns the next row in this result.
*
* @return the next row in this result.
*/
@Override
Map next();
/**
* Closes the result, freeing up any resources held by the result.
*
* This is an idempotent operation, invoking it multiple times has the same effect as invoking it exactly once.
* It is thus safe (and even encouraged, for style and simplicity) to invoke this method even after consuming all
* rows in the result through the {@link #next() next-method}.
*/
@Override
void close();
/**
* Statistics about the effects of the query.
*
* @return statistics about the effects of the query.
*/
QueryStatistics getQueryStatistics();
/**
* Returns a description of the query plan used to produce this result.
*
* Retrieving a description of the execution plan that was executed is always possible, regardless of whether the
* query requested a plan or not. For implementing a client with the ability to present the plan to the user, it is
* useful to be able to tell if the query requested a description of the plan or not. For these purposes the
* {@link QueryExecutionType#requestedExecutionPlanDescription()}-method is used.
*
* Being able to invoke this method, regardless of whether the user requested the plan or not is useful for
* purposes of debugging queries in applications.
*
* @return a description of the query plan used to produce this result.
*/
ExecutionPlanDescription getExecutionPlanDescription();
/**
* Provides a textual representation of the query result.
*
* The execution result represented by this object will be consumed in its entirety after this method is called.
* Calling any of the other iterating methods on it should not be expected to return any results.
*
*
* @return the execution result formatted as a string
*/
String resultAsString();
/**
* Provides a textual representation of the query result to the provided {@link java.io.PrintWriter}.
*
* The execution result represented by this object will be consumed in its entirety after this method is called.
* Calling any of the other iterating methods on it should not be expected to return any results.
*
*
* @param writer the {@link java.io.PrintWriter} to receive the textual representation of the query result.
*/
void writeAsStringTo(PrintWriter writer);
/** Removing rows from the result is not supported. */
@Override
void remove();
/**
* Provides notifications about the query producing this result.
*
* Notifications can be warnings about problematic queries or other valuable information that can be
* presented in a client.
*
* @return an iterable of all notifications created when running the query.
*/
Iterable getNotifications();
/**
* Provides GQL-status object for the query execution producing this result.
*
* GQL-status objects contains diagnostic information and the status of the query execution,
* including warnings about problematic queries or other valuable information that can be
* presented in a client.
*
* @return an iterable of all GQL-status objects created when running the query.
*/
Iterable getGqlStatusObjects();
/**
* Visits all rows in this Result by iterating over them.
*
* This is an alternative to using the iterator form of Result. Using the visitor is better from a object
* creation perspective.
*
* @param visitor the ResultVisitor instance that will see the results of the visit.
* @param the type of the exception that might get thrown
* @throws VisitationException if the {@code visit(ResultRow)} method of {@link ResultVisitor} throws such an
* exception.
*/
void accept(ResultVisitor visitor)
throws VisitationException;
/**
* Describes a row of a result. The contents of this object is only stable during the
* call to the {@code visit(ResultRow)} method of {@link ResultVisitor}.
* The data it contains can change between calls to the {@code visit(ResultRow)} method.
* Instances of this type should thus not be saved
* for later use, or shared with other threads, rather the content should be copied.
*/
interface ResultRow {
// TODO: Type safe getters for collections and maps?
Node getNode(String key);
Relationship getRelationship(String key);
Object get(String key);
String getString(String key);
Number getNumber(String key);
Boolean getBoolean(String key);
Path getPath(String key);
}
/**
* This is the visitor interface you need to implement to use the {@link Result#accept(ResultVisitor)} method.
*/
interface ResultVisitor {
/**
* Visits the specified row.
*
* @param row the row to visit. The row object is only guaranteed to be stable until flow of control has
* returned from this method.
* @return true if the next row should also be visited. Returning false will terminate the iteration of
* result rows.
* @throws VisitationException if there is a problem in the execution of this method. This exception will close
* the result being visited, and the exception will propagate out through the
* {@linkplain #accept(ResultVisitor) accept method}.
*/
boolean visit(ResultRow row) throws VisitationException;
}
}