gdal vector partition: make --fields optional

Fixes OSGeo#13758

Author: rouault

apps/gdalalg_vector_partition.cpp

@@ -30,6 +30,7 @@ constexpr int DIRECTORY_CREATION_MODE = 0755;
 constexpr const char *NULL_MARKER = "__HIVE_DEFAULT_PARTITION__";
 
 constexpr const char *DEFAULT_PATTERN_HIVE = "part_%010d";
+constexpr const char *DEFAULT_PATTERN_FLAT_NO_FIELD = "{LAYER_NAME}_%010d";
 constexpr const char *DEFAULT_PATTERN_FLAT = "{LAYER_NAME}_{FIELD_VALUE}_%010d";
 
 constexpr char DIGIT_ZERO = '0';
@@ -84,8 +85,8 @@ GDALVectorPartitionAlgorithm::GDALVectorPartitionAlgorithm(bool standaloneStep)
     AddLayerCreationOptionsArg(&m_layerCreationOptions);
 
     AddArg("field", 0,
-           _("Attribute or geometry field(s) on which to partition"), &m_fields)
-        .SetRequired();
+           _("Attribute or geometry field(s) on which to partition"),
+           &m_fields);
     AddArg("scheme", 0, _("Partitioning scheme"), &m_scheme)
         .SetChoices(SCHEME_HIVE, SCHEME_FLAT)
         .SetDefault(m_scheme);
@@ -205,6 +206,20 @@ GDALVectorPartitionAlgorithm::GDALVectorPartitionAlgorithm(bool standaloneStep)
         .SetMinValueIncluded(1)
         .SetDefault(m_transactionSize)
         .SetHidden();
+
+    AddValidationAction(
+        [this]()
+        {
+            if (m_fields.empty() && m_featureLimit == 0 && m_maxFileSize == 0)
+            {
+                ReportError(
+                    CE_Failure, CPLE_IllegalArg,
+                    "When 'fields' argument is not specified, "
+                    "'feature-limit' and/or 'max-file-size' must be specified");
+                return false;
+            }
+            return true;
+        });
 }
 
 /************************************************************************/
@@ -384,7 +399,8 @@ static bool GetCurrentOutputLayer(
         !osPatternIn.empty() ? osPatternIn
         : osScheme == GDALVectorPartitionAlgorithm::SCHEME_HIVE
             ? DEFAULT_PATTERN_HIVE
-            : DEFAULT_PATTERN_FLAT;
+        : osKey.empty() ? DEFAULT_PATTERN_FLAT_NO_FIELD
+                        : DEFAULT_PATTERN_FLAT;
 
     bool bLimitReached = false;
     bool bOpenOrCreateNewFile = true;

autotest/utilities/test_gdalalg_vector_partition.py

@@ -1210,3 +1210,40 @@ def test_gdalalg_vector_partition_geometry_multi_geom_fields(tmp_vsimem):
             lyr.GetFeature(1).GetGeomFieldRef(1).ExportToIsoWkt()
             == "LINESTRING (5 6,7 8)"
         )
+
+
+@pytest.mark.require_driver("GPKG")
+def test_gdalalg_vector_partition_no_fields(tmp_vsimem):
+
+    with pytest.raises(
+        Exception,
+        match="When 'fields' argument is not specified, 'feature-limit' and/or 'max-file-size' must be specified",
+    ):
+        gdal.alg.vector.partition(
+            input=src_ds(), output=tmp_vsimem / "out", output_format="GPKG"
+        )
+
+    gdal.alg.vector.partition(
+        input=src_ds(), output=tmp_vsimem / "out", feature_limit=2, output_format="GPKG"
+    )
+
+    assert gdal.ReadDir(tmp_vsimem / "out" / "test") == [
+        "part_0000000001.gpkg",
+        "part_0000000002.gpkg",
+    ]
+
+    gdal.RmdirRecursive(tmp_vsimem / "out")
+
+    gdal.alg.vector.partition(
+        input=src_ds(),
+        output=tmp_vsimem / "out",
+        feature_limit=2,
+        output_format="GPKG",
+        scheme="flat",
+    )
+
+    assert gdal.ReadDir(tmp_vsimem / "out") == [
+        "non%20spatial_0000000001.gpkg",
+        "test_0000000001.gpkg",
+        "test_0000000002.gpkg",
+    ]

doc/source/programs/gdal_vector_partition.rst

@@ -22,7 +22,8 @@ Description
 
 :program:`gdal vector partition` dispatches features into different
 files, depending on the values the feature take on a subset of attribute or
-geometry fields specified by the user.
+geometry fields specified by the user and/or by limiting each output layer
+to a maximum number of features and/or a maximum file size.
 
 Two partitioning schemes are available:
 
@@ -62,7 +63,7 @@ Program-Specific Options
 
 .. option:: --field <FIELD-NAME>
 
-    Fields(s) on which to partition. [required]
+    Fields(s) on which to partition
 
     Only attribute fields of type String, Integer and Integer64 are allowed.
     The order into which fields are specified matter to determine the directory
@@ -73,6 +74,10 @@ Program-Specific Options
     geometry fields is done on the geometry type. This can be useful for file
     formats where a single geometry type per layer is allowed.
 
+    Starting with GDAL 3.13, :option:`--field` is no longer required, but when
+    it is not specified, :option:`--feature-limit` and/or :option:`--max-file-size`
+    must be specified.
+
 .. option:: --max-file-size <MAX-FILE-SIZE>
 
     Maximum file size (MB or GB suffix can be used). By default, unlimited.
@@ -168,3 +173,17 @@ Examples
    .. code-block:: bash
 
         $ gdal vector pipeline ! read input.gpkg ! set-geom-type --multi ! partition out_directory --scheme flat --field OGR_GEOMETRY --format "ESRI Shapefile"
+
+.. example::
+   :title: Split a file into files with at most 100,000 features.
+
+   .. code-block:: bash
+
+        $ gdal vector partition world_cities.gpkg out_directory --feature-limit 100000 --scheme flat --format Parquet
+
+.. example::
+   :title: Sort a file spatially and split it into files with at most 100,000 features.
+
+   .. code-block:: bash
+
+        $ gdal vector pipeline read world_cities.gpkg ! sort ! partition out_directory --feature-limit 100000 --scheme flat --format Parquet