[sis] 01/02: Add a test and comment explaining why resolving links is an important optimization. It makes the difference between using or not a database index.

[desruisseaux]

This is an automated email from the ASF dual-hosted git repository.

desruisseaux pushed a commit to branch geoapi-4.0
in repository https://gitbox.apache.org/repos/asf/sis.git

commit f072a37f8cd31461a3f9ea4a55146ee9aa37a79b
Author: Martin Desruisseaux <martin.desruisse...@geomatys.com>
AuthorDate: Sun Dec 26 23:45:14 2021 +0100

    Add a test and comment explaining why resolving links is an important 
optimization.
    It makes the difference between using or not a database index.
---
 .../src/main/java/org/apache/sis/filter/PropertyValue.java       | 6 ++++--
 .../java/org/apache/sis/internal/sql/feature/FeatureStream.java  | 2 ++
 .../src/test/java/org/apache/sis/storage/sql/SQLStoreTest.java   | 9 +++++++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git 
a/core/sis-feature/src/main/java/org/apache/sis/filter/PropertyValue.java 
b/core/sis-feature/src/main/java/org/apache/sis/filter/PropertyValue.java
index 8a20ddc..89714ff 100644
--- a/core/sis-feature/src/main/java/org/apache/sis/filter/PropertyValue.java
+++ b/core/sis-feature/src/main/java/org/apache/sis/filter/PropertyValue.java
@@ -167,8 +167,10 @@ abstract class PropertyValue<V> extends 
LeafExpression<Feature,V> implements Val
         }
 
         /**
-         * If the evaluated property is a link, replaces this expression
-         * by a more direct reference to the target property.
+         * If the evaluated property is a link, replaces this expression by a 
more direct reference
+         * to the target property. This optimization is important for allowing 
{@code SQLStore} to
+         * put the column name in the SQL {@code WHERE} clause. It makes the 
difference between
+         * using or not the database index.
          */
         @Override
         public Expression<Feature,?> optimize(final Optimization optimization) 
{
diff --git 
a/storage/sis-sqlstore/src/main/java/org/apache/sis/internal/sql/feature/FeatureStream.java
 
b/storage/sis-sqlstore/src/main/java/org/apache/sis/internal/sql/feature/FeatureStream.java
index 2660249..850cde5 100644
--- 
a/storage/sis-sqlstore/src/main/java/org/apache/sis/internal/sql/feature/FeatureStream.java
+++ 
b/storage/sis-sqlstore/src/main/java/org/apache/sis/internal/sql/feature/FeatureStream.java
@@ -405,6 +405,8 @@ final class FeatureStream extends DeferredStream<Feature> {
 
     /**
      * Returns a string representation of this stream for debugging purposes.
+     * The returned string tells whether filtering and sorting are done using
+     * SQL statement, Java code, or a mix of both.
      */
     @Override
     public String toString() {
diff --git 
a/storage/sis-sqlstore/src/test/java/org/apache/sis/storage/sql/SQLStoreTest.java
 
b/storage/sis-sqlstore/src/test/java/org/apache/sis/storage/sql/SQLStoreTest.java
index a1ee95e..f36f861 100644
--- 
a/storage/sis-sqlstore/src/test/java/org/apache/sis/storage/sql/SQLStoreTest.java
+++ 
b/storage/sis-sqlstore/src/test/java/org/apache/sis/storage/sql/SQLStoreTest.java
@@ -445,11 +445,20 @@ public final strictfp class SQLStoreTest extends TestCase 
{
         final FeatureSet   countries   = dataset.findResource("Countries");
         final FeatureQuery query       = new FeatureQuery();
         query.setSelection(FF.equal(FF.property("sis:identifier"), 
FF.literal("CAN")));
+        final String executionMode;
         final Object[] names;
         try (Stream<Feature> features = 
countries.subset(query).features(false)) {
+            executionMode = features.toString();
             names = features.map(f -> 
f.getPropertyValue(desiredProperty)).toArray();
         }
         assertArrayEquals(expectedValues, names);
+        /*
+         * Verify that the query is executed with a SQL statement, not with 
Java code.
+         * The use of SQL is made possible by the replacement of 
"sis:identifier" link
+         * by a reference to "code" column. If that replacement is not 
properly done,
+         * then the "predicates" value would be "Java" instead of "SQL".
+         */
+        assertEquals("FeatureStream[table=“Countries”, predicates=“SQL”]", 
executionMode);
     }
 
     /**