[GitHub] [groovy] muse-dev[bot] commented on a change in pull request #1395: [GEP] Create a LINQ-like DSL

[GitBox <gi...@apache.org>]

muse-dev[bot] commented on a change in pull request #1395:
URL: https://github.com/apache/groovy/pull/1395#discussion_r499265164



##########
File path: subprojects/groovy-linq/src/main/java/org/apache/groovy/linq/provider/QueryableCollection.java
##########
@@ -0,0 +1,244 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package org.apache.groovy.linq.provider;
+
+import groovy.lang.Tuple;
+import groovy.lang.Tuple2;
+import org.apache.groovy.linq.Queryable;
+
+import java.math.BigDecimal;
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.function.BiPredicate;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+/**
+ * Represents the queryable collections
+ *
+ * @param <T> the type of Queryable element
+ * @since 4.0.0
+ */
+public class QueryableCollection<T> implements Queryable<T>, Iterable<T> {
+    private final Iterable<T> sourceIterable;
+    private Stream<T> sourceStream;
+
+    public static <T> Queryable<T> from(Iterable<T> sourceIterable) {
+        return new QueryableCollection<>(sourceIterable);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <T> Queryable<T> from(Stream<? extends T> sourceStream) {
+        Iterable<T> sourceIterable = (Iterable<T>) toIterable(sourceStream);
+        return from(sourceIterable);
+    }
+
+    private QueryableCollection(Iterable<T> sourceIterable) {
+        this.sourceIterable = sourceIterable;
+        this.sourceStream = toStream(sourceIterable);
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return sourceIterable.iterator();
+    }
+
+    @Override
+    public <U> Queryable<Tuple2<T, U>> innerJoin(Queryable<? extends U> queryable, BiPredicate<? super T, ? super U> joiner) {
+        Stream<Tuple2<T, U>> stream =
+                this.stream()
+                        .flatMap(p ->
+                                queryable.stream()
+                                        .filter(c -> joiner.test(p, c))
+                                        .map(c -> Tuple.tuple(p, c)));
+
+        return from(stream);
+    }
+
+    @Override
+    public <U> Queryable<Tuple2<T, U>> leftJoin(Queryable<? extends U> queryable, BiPredicate<? super T, ? super U> joiner) {
+        return outerJoin(this, queryable, joiner);
+    }
+
+    @Override
+    public <U> Queryable<Tuple2<T, U>> rightJoin(Queryable<? extends U> queryable, BiPredicate<? super T, ? super U> joiner) {
+        return outerJoin(queryable, this, (a, b) -> joiner.test(b, a)).select(e -> Tuple.tuple(e.getV2(), e.getV1()));
+    }
+
+    @Override
+    public <U> Queryable<Tuple2<T, U>> crossJoin(Queryable<? extends U> queryable) {
+        Stream<Tuple2<T, U>> stream =
+                this.stream()
+                        .flatMap(p ->
+                                queryable.stream()
+                                        .map(c -> Tuple.tuple(p, c)));
+
+        return from(stream);
+    }
+
+    @Override
+    public Queryable<T> where(Predicate<? super T> filter) {
+        Stream<T> stream = this.stream().filter(filter::test);
+
+        return from(stream);
+    }
+
+    @Override
+    public <K> Queryable<Tuple2<K, Queryable<T>>> groupBy(Function<? super T, ? extends K> classifier, BiPredicate<? super K, ? super Queryable<? extends T>> having) {
+        Stream<Tuple2<K, Queryable<T>>> stream =
+                this.stream()
+                        .collect(Collectors.groupingBy(classifier, Collectors.toList()))
+                        .entrySet().stream()
+                        .filter(m -> having.test(m.getKey(), from(m.getValue())))
+                        .map(m -> Tuple.tuple(m.getKey(), from(m.getValue())));
+
+        return from(stream);
+    }
+
+    @Override
+    public <U extends Comparable<? super U>> Queryable<T> orderBy(Order<? super T, ? extends U>... orders) {
+        Comparator<T> comparator = null;
+        for (int i = 0, n = orders.length; i < n; i++) {
+            Order<? super T, ? extends U> order = orders[i];
+            Comparator<U> ascOrDesc = order.isAsc() ? Comparator.naturalOrder() : Comparator.reverseOrder();
+            comparator =
+                    0 == i
+                            ? Comparator.comparing(order.getKeyExtractor(), ascOrDesc)
+                            : comparator.thenComparing(order.getKeyExtractor(), ascOrDesc);
+        }
+
+        if (null == comparator) {
+            return this;
+        }
+
+        return from(this.stream().sorted(comparator));
+    }
+
+    @Override
+    public Queryable<T> limit(int offset, int size) {
+        Stream<T> stream = this.stream().skip(offset).limit(size);
+
+        return from(stream);
+    }
+
+    @Override
+    public <U> Queryable<U> select(Function<? super T, ? extends U> mapper) {
+        Stream<U> stream = this.stream().map(mapper);
+
+        return from(stream);
+    }
+
+    @Override
+    public Queryable<T> distinct() {
+        Stream<? extends T> stream = this.stream().distinct();
+
+        return from(stream);
+    }
+
+    @Override
+    public Queryable<T> unionAll(Queryable<? extends T> queryable) {
+        Stream<T> stream = Stream.concat(this.stream(), queryable.stream());
+
+        return from(stream);
+    }
+
+    @Override
+    public Queryable<T> intersect(Queryable<? extends T> queryable) {
+        Stream<T> stream = this.stream().filter(a -> queryable.stream().anyMatch(b -> b.equals(a))).distinct();
+
+        return from(stream);
+    }
+
+    @Override
+    public Queryable<T> minus(Queryable<? extends T> queryable) {
+        Stream<T> stream = this.stream().filter(a -> queryable.stream().noneMatch(b -> b.equals(a))).distinct();
+
+        return from(stream);
+    }
+
+    @Override
+    public List<T> toList() {
+        return stream().collect(Collectors.toList());
+    }
+
+    @Override
+    public Stream<T> stream() {
+        try {
+            sourceStream = sourceStream.peek(e -> {}); // check whether the stream is usable
+        } catch (IllegalStateException ex) {
+            sourceStream = toStream(sourceIterable);  // we have to create new stream every time because Java stream can not be reused
+        }
+
+        return sourceStream;
+    }
+
+    @Override
+    public int count() {
+        return toList().size();
+    }
+
+    @Override
+    public BigDecimal sum(Function<? super T, BigDecimal> mapper) {
+        return this.stream().map(mapper).reduce(BigDecimal.ZERO, BigDecimal::add);
+    }
+
+    private static <T, U> Queryable<Tuple2<T, U>> outerJoin(Queryable<? extends T> queryable1, Queryable<? extends U> queryable2, BiPredicate<? super T, ? super U> joiner) {
+        Stream<Tuple2<T, U>> stream =
+                queryable1.stream()
+                        .flatMap(p ->
+                                queryable2.stream()
+                                        .map(c -> joiner.test(p, c) ? c : null)
+                                        .reduce(new LinkedList<U>(), (r, e) -> {

Review comment:
       *JdkObsolete:*  It is very rare for LinkedList to out-perform ArrayList or ArrayDeque. Avoid it unless you're willing to invest a lot of time into benchmarking. Caveat: LinkedList supports null elements, but ArrayDeque does not.




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