From 63ff050e4d48f8b997905e9e0a11d944ea6038a6 Mon Sep 17 00:00:00 2001
From: "Brian S. O'Neill" <bronee@gmail.com>
Date: Mon, 14 Apr 2008 03:18:32 +0000
Subject: Support query fetch limits.

---
 .../com/amazon/carbonado/qe/AbstractQuery.java     | 22 +++++++++++++++++++++
 .../amazon/carbonado/qe/AbstractQueryExecutor.java | 23 +++++++++++++++++++++-
 .../carbonado/qe/DelegatedQueryExecutor.java       |  4 ++++
 .../java/com/amazon/carbonado/qe/EmptyQuery.java   | 16 +++++++++++++++
 .../com/amazon/carbonado/qe/QueryExecutor.java     |  7 +++++++
 .../com/amazon/carbonado/qe/StandardQuery.java     | 23 ++++++++++++++++++++++
 6 files changed, 94 insertions(+), 1 deletion(-)

(limited to 'src/main/java/com/amazon/carbonado/qe')

diff --git a/src/main/java/com/amazon/carbonado/qe/AbstractQuery.java b/src/main/java/com/amazon/carbonado/qe/AbstractQuery.java
index 7639348..767b039 100644
--- a/src/main/java/com/amazon/carbonado/qe/AbstractQuery.java
+++ b/src/main/java/com/amazon/carbonado/qe/AbstractQuery.java
@@ -129,4 +129,26 @@ public abstract class AbstractQuery<S extends Storable> implements Query<S>, App
 
     @Override
     public abstract boolean equals(Object obj);
+
+    /**
+     * Called by sliced fetch to ensure that arguments are valid.
+     *
+     * @return false if from is 0 and to is null
+     * @throws IllegalArgumentException if arguments are invalid
+     * @since 1.2
+     */
+    protected boolean checkSliceArguments(long from, Long to) {
+        if (from < 0) {
+            throw new IllegalArgumentException("Slice from is negative: " + from);
+        }
+        if (to == null) {
+            if (from == 0) {
+                return false;
+            }
+        } else if (from > to) {
+            throw new IllegalArgumentException
+                ("Slice from is more than to: " + from + " > " + to);
+        }
+        return true;
+    }
 }
diff --git a/src/main/java/com/amazon/carbonado/qe/AbstractQueryExecutor.java b/src/main/java/com/amazon/carbonado/qe/AbstractQueryExecutor.java
index dc67fc1..8a8a127 100644
--- a/src/main/java/com/amazon/carbonado/qe/AbstractQueryExecutor.java
+++ b/src/main/java/com/amazon/carbonado/qe/AbstractQueryExecutor.java
@@ -24,6 +24,9 @@ import com.amazon.carbonado.Cursor;
 import com.amazon.carbonado.FetchException;
 import com.amazon.carbonado.Storable;
 
+import com.amazon.carbonado.cursor.LimitCursor;
+import com.amazon.carbonado.cursor.SkipCursor;
+
 import com.amazon.carbonado.filter.FilterValues;
 
 /**
@@ -37,7 +40,25 @@ public abstract class AbstractQueryExecutor<S extends Storable> implements Query
     }
 
     /**
-     * Counts results by opening a cursor and skipping entries.
+     * Produces a slice via skip and limit cursors. Subclasses are encouraged
+     * to override with a more efficient implementation.
+     *
+     * @since 1.2
+     */
+    public Cursor<S> fetch(FilterValues<S> values, long from, Long to) throws FetchException {
+        Cursor<S> cursor = fetch(values);
+        if (from > 0) {
+            cursor = new SkipCursor<S>(cursor, from);
+        }
+        if (to != null) {
+            cursor = new LimitCursor<S>(cursor, to - from);
+        }
+        return cursor;
+    }
+
+    /**
+     * Counts results by opening a cursor and skipping entries. Subclasses are
+     * encouraged to override with a more efficient implementation.
      */
     public long count(FilterValues<S> values) throws FetchException {
         Cursor<S> cursor = fetch(values);
diff --git a/src/main/java/com/amazon/carbonado/qe/DelegatedQueryExecutor.java b/src/main/java/com/amazon/carbonado/qe/DelegatedQueryExecutor.java
index b4bc0a3..3ec209d 100644
--- a/src/main/java/com/amazon/carbonado/qe/DelegatedQueryExecutor.java
+++ b/src/main/java/com/amazon/carbonado/qe/DelegatedQueryExecutor.java
@@ -95,6 +95,10 @@ public class DelegatedQueryExecutor<S extends Storable> implements QueryExecutor
         return applyFilterValues(values).fetch();
     }
 
+    public Cursor<S> fetch(FilterValues<S> values, long from, Long to) throws FetchException {
+        return applyFilterValues(values).fetch(from, to);
+    }
+
     public long count(FilterValues<S> values) throws FetchException {
         return applyFilterValues(values).count();
     }
diff --git a/src/main/java/com/amazon/carbonado/qe/EmptyQuery.java b/src/main/java/com/amazon/carbonado/qe/EmptyQuery.java
index f3d54f5..9754019 100644
--- a/src/main/java/com/amazon/carbonado/qe/EmptyQuery.java
+++ b/src/main/java/com/amazon/carbonado/qe/EmptyQuery.java
@@ -212,6 +212,14 @@ public final class EmptyQuery<S extends Storable> extends AbstractQuery<S> {
         return EmptyCursor.the();
     }
 
+    /**
+     * Always returns an {@link EmptyCursor}.
+     */
+    public Cursor<S> fetch(long from, Long to) {
+        checkSliceArguments(from, to);
+        return EmptyCursor.the();
+    }
+
     /**
      * Always returns an {@link EmptyCursor}.
      */
@@ -219,6 +227,14 @@ public final class EmptyQuery<S extends Storable> extends AbstractQuery<S> {
         return EmptyCursor.the();
     }
 
+    /**
+     * Always returns an {@link EmptyCursor}.
+     */
+    public Cursor<S> fetchAfter(S start, long from, Long to) {
+        checkSliceArguments(from, to);
+        return EmptyCursor.the();
+    }
+
     /**
      * Always throws {@link PersistNoneException}.
      */
diff --git a/src/main/java/com/amazon/carbonado/qe/QueryExecutor.java b/src/main/java/com/amazon/carbonado/qe/QueryExecutor.java
index b0ab801..6b5a864 100644
--- a/src/main/java/com/amazon/carbonado/qe/QueryExecutor.java
+++ b/src/main/java/com/amazon/carbonado/qe/QueryExecutor.java
@@ -45,6 +45,13 @@ public interface QueryExecutor<S extends Storable> {
      */
     Cursor<S> fetch(FilterValues<S> values) throws FetchException;
 
+    /**
+     * Returns a new cursor using the given filter values and slice.
+     *
+     * @since 1.2
+     */
+    Cursor<S> fetch(FilterValues<S> values, long from, Long to) throws FetchException;
+
     /**
      * Counts the query results using the given filter values.
      */
diff --git a/src/main/java/com/amazon/carbonado/qe/StandardQuery.java b/src/main/java/com/amazon/carbonado/qe/StandardQuery.java
index 5596c32..10fdf43 100644
--- a/src/main/java/com/amazon/carbonado/qe/StandardQuery.java
+++ b/src/main/java/com/amazon/carbonado/qe/StandardQuery.java
@@ -217,6 +217,18 @@ public abstract class StandardQuery<S extends Storable> extends AbstractQuery<S>
         }
     }
 
+    public Cursor<S> fetch(long from, Long to) throws FetchException {
+        if (!checkSliceArguments(from, to)) {
+            return fetch();
+        }
+        try {
+            QueryHints hints = QueryHints.emptyHints().with(QueryHint.CONSUME_SLICE);
+            return executorFactory().executor(mFilter, mOrdering, hints).fetch(mValues, from, to);
+        } catch (RepositoryException e) {
+            throw e.toFetchException();
+        }
+    }
+
     public Cursor<S> fetchAfter(S start) throws FetchException {
         OrderingList<S> orderings;
         if (start == null || (orderings = mOrdering).size() == 0) {
@@ -225,6 +237,17 @@ public abstract class StandardQuery<S extends Storable> extends AbstractQuery<S>
         return buildAfter(start, orderings).fetch();
     }
 
+    public Cursor<S> fetchAfter(S start, long from, Long to) throws FetchException {
+        if (!checkSliceArguments(from, to)) {
+            return fetchAfter(start);
+        }
+        OrderingList<S> orderings;
+        if (start == null || (orderings = mOrdering).size() == 0) {
+            return fetch(from, to);
+        }
+        return buildAfter(start, orderings).fetch(from, to);
+    }
+
     private Query<S> buildAfter(S start, OrderingList<S> orderings) throws FetchException {
         Class<S> storableType = getStorableType();
         Filter<S> orderFilter = Filter.getClosedFilter(storableType);
-- 
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