ENH: Add append support to write functions

.github/workflows/docker-gdal.yml

@@ -17,6 +17,7 @@ jobs:
     name: GDAL ${{ matrix.container }}
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
         container:
           - "osgeo/gdal:ubuntu-small-latest" # >= python 3.8.10

CHANGES.md

@@ -9,6 +9,8 @@
     This can be enabled by passing `use_arrow=True` to `pyogrio.read_dataframe`
     (or by using `pyogrio.raw.read_arrow` directly), and provides a further
     speed-up (#155, #191).
+-   Support for appending to an existing data source when supported by GDAL by
+    passing `append=True` to `pyogrio.write_dataframe` (#197).
 
 ## O.4.2
 

docs/source/introduction.md

@@ -24,10 +24,15 @@ Not all geometry or field types may be supported for all drivers.
 {...'GeoJSON': 'rw', 'GeoJSONSeq': 'rw',...}
 ```
 
-Drivers that are not known to be supported are listed with `"?"` for capabilities.
-Drivers that are known to support write capability end in `"w"`.
+Drivers that support write capability in your version of GDAL end in `"w"`.
+Certain drivers that are known to be unsupported in Pyogrio are disabled for
+write capabilities.
 
-To find subsets of drivers that have known support:
+NOTE: not all drivers support writing the contents of a GeoDataFrame; you may
+encounter errors due to unsupported data types, unsupported geometry types,
+or other driver-related errors when writing to a data source.
+
+To find subsets of drivers that support read or write capabilities:
 
 ```python
 >>> list_drivers(read=True)
@@ -38,8 +43,13 @@ See the full list of [drivers](https://gdal.org/drivers/vector/index.html) for
 more information about specific drivers, including their write support and
 configuration options.
 
-You can certainly try to read or write using unsupported drivers that are
-available in your installation, but you may encounter errors.
+The following drivers are known to be well-supported and tested in Pyogrio:
+
+-   `ESRI Shapefile`
+-   `FlatGeobuf`
+-   `GeoJSON`
+-   `GeoJSONSeq`
+-   `GPKG`
 
 ## List available layers
 
@@ -328,6 +338,23 @@ If you want to write another file format supported by GDAL or if you want to
 overrule the default driver for an extension, you can specify the driver with the
 `driver` keyword, e.g. `driver="GPKG"`.
 
+## Appending to an existing data source
+
+Certain drivers may support the ability to append records to an existing data
+source. See the
+[GDAL driver listing](https://gdal.org/drivers/vector/index.html)
+for details about the capabilities of a driver for your version of GDAL.
+
+```
+>>> write_dataframe(df, "/tmp/existing_file.gpkg", append=True)
+```
+
+NOTE: the data structure of the data frame you are appending to the existing
+data source must exactly match the structure of the existing data source.
+
+NOTE: not all drivers that support write capabilities support append
+capabilities for a given GDAL version.
+
 ## Reading from compressed files / archives
 
 GDAL supports reading directly from an archive, such as a zipped folder, without

pyogrio/_io.pyx

@@ -125,7 +125,6 @@ cdef void* ogr_open(const char* path_c, int mode, options) except NULL:
     else:
         flags |= GDAL_OF_READONLY
 
-    # TODO: other open opts from fiona
     open_opts = CSLAddNameValue(open_opts, "VALIDATE_OPEN_OPTIONS", "NO")
 
     try:
@@ -1329,12 +1328,12 @@ cdef infer_field_types(list dtypes):
     return field_types
 
 
-# TODO: handle updateable data sources, like GPKG
 # TODO: set geometry and field data as memory views?
 def ogr_write(
     str path, str layer, str driver, geometry, field_data, fields,
     str crs, str geometry_type, str encoding, object dataset_kwargs,
     object layer_kwargs, bint promote_to_multi=False, bint nan_as_null=True,
+    bint append=False
 ):
     cdef const char *path_c = NULL
     cdef const char *layer_c = NULL
@@ -1377,33 +1376,37 @@ def ogr_write(
     if not layer:
         layer = os.path.splitext(os.path.split(path)[1])[0]
 
-    layer_b = layer.encode('UTF-8')
-    layer_c = layer_b
 
     # if shapefile, GeoJSON, or FlatGeobuf, always delete first
     # for other types, check if we can create layers
     # GPKG might be the only multi-layer writeable type.  TODO: check this
     if driver in ('ESRI Shapefile', 'GeoJSON', 'GeoJSONSeq', 'FlatGeobuf') and os.path.exists(path):
-        os.unlink(path)
+        if not append:
+            os.unlink(path)
 
-    # TODO: invert this: if exists then try to update it, if that doesn't work then always create
+    layer_exists = False
     if os.path.exists(path):
         try:
             ogr_dataset = ogr_open(path_c, 1, None)
 
-            # If layer exists, delete it.
             for i in range(GDALDatasetGetLayerCount(ogr_dataset)):
                 name = OGR_L_GetName(GDALDatasetGetLayer(ogr_dataset, i))
                 if layer == name.decode('UTF-8'):
                     layer_idx = i
                     break
 
             if layer_idx >= 0:
-                GDALDatasetDeleteLayer(ogr_dataset, layer_idx)
+                layer_exists = True
+
+                if not append:
+                    GDALDatasetDeleteLayer(ogr_dataset, layer_idx)
+
+        except DataSourceError as exc:
+            # open failed
+            if append:
+                raise exc
 
-        except DataSourceError:
-            # open failed, so create from scratch
-            # force delete it first
+            # otherwise create from scratch
             os.unlink(path)
             ogr_dataset = NULL
 
@@ -1416,48 +1419,58 @@ def ogr_write(
 
         ogr_dataset = ogr_create(path_c, driver_c, dataset_options)
 
-    ### Create the CRS
-    if crs is not None:
-        try:
-            ogr_crs = create_crs(crs)
+    # if we are not appending to an existing layer, we need to create
+    # the layer and all associated properties (CRS, field defs, etc)
+    create_layer = not (append and layer_exists)
 
-        except Exception as exc:
-            OGRReleaseDataSource(ogr_dataset)
-            ogr_dataset = NULL
-            if dataset_options != NULL:
-                CSLDestroy(<char**>dataset_options)
-                dataset_options = NULL
-            raise exc
+    ### Create the layer
+    if create_layer:
+        # Create the CRS
+        if crs is not None:
+            try:
+                ogr_crs = create_crs(crs)
+
+            except Exception as exc:
+                OGRReleaseDataSource(ogr_dataset)
+                ogr_dataset = NULL
+                if dataset_options != NULL:
+                    CSLDestroy(<char**>dataset_options)
+                    dataset_options = NULL
+                raise exc
+
+        # Setup layer creation options
+        if not encoding:
+            encoding = locale.getpreferredencoding()
+
+        if driver == 'ESRI Shapefile':
+            # Fiona only sets encoding for shapefiles; other drivers do not support
+            # encoding as an option.
+            encoding_b = encoding.upper().encode('UTF-8')
+            encoding_c = encoding_b
+            layer_options = CSLSetNameValue(layer_options, "ENCODING", encoding_c)
+
+        # Setup other layer creation options
+        for k, v in layer_kwargs.items():
+            k = k.encode('UTF-8')
+            v = v.encode('UTF-8')
+            layer_options = CSLAddNameValue(layer_options, <const char *>k, <const char *>v)
 
+        ### Get geometry type
+        # TODO: this is brittle for 3D / ZM / M types
+        # TODO: fail on M / ZM types
+        geometry_code = get_geometry_type_code(geometry_type or "Unknown")
 
-    ### Create options
-    if not encoding:
-        encoding = locale.getpreferredencoding()
+    try:
+        if create_layer:
+            layer_b = layer.encode('UTF-8')
+            layer_c = layer_b
 
-    if driver == 'ESRI Shapefile':
-        # Fiona only sets encoding for shapefiles; other drivers do not support
-        # encoding as an option.
-        encoding_b = encoding.upper().encode('UTF-8')
-        encoding_c = encoding_b
-        layer_options = CSLSetNameValue(layer_options, "ENCODING", encoding_c)
-
-    # Setup other layer creation options
-    for k, v in layer_kwargs.items():
-        k = k.encode('UTF-8')
-        v = v.encode('UTF-8')
-        layer_options = CSLAddNameValue(layer_options, <const char *>k, <const char *>v)
-
-    ### Get geometry type
-    # TODO: this is brittle for 3D / ZM / M types
-    # TODO: fail on M / ZM types
-    geometry_code = get_geometry_type_code(geometry_type or "Unknown")
+            ogr_layer = exc_wrap_pointer(
+                    GDALDatasetCreateLayer(ogr_dataset, layer_c, ogr_crs,
+                            geometry_code, layer_options))
 
-    ### Create the layer
-    try:
-        ogr_layer = exc_wrap_pointer(
-                GDALDatasetCreateLayer(ogr_dataset, layer_c, ogr_crs,
-                                       <OGRwkbGeometryType>geometry_code,
-                                       layer_options))
+        else:
+            ogr_layer = exc_wrap_pointer(get_ogr_layer(ogr_dataset, layer))
 
     except Exception as exc:
         OGRReleaseDataSource(ogr_dataset)
@@ -1470,51 +1483,54 @@ def ogr_write(
             ogr_crs = NULL
 
         if dataset_options != NULL:
-            CSLDestroy(<char**>dataset_options)
+            CSLDestroy(dataset_options)
             dataset_options = NULL
 
         if layer_options != NULL:
-            CSLDestroy(<char**>layer_options)
+            CSLDestroy(layer_options)
             layer_options = NULL
 
     ### Create the fields
     field_types = infer_field_types([field.dtype for field in field_data])
-    for i in range(num_fields):
-        field_type, field_subtype, width, precision = field_types[i]
 
-        name_b = fields[i].encode(encoding)
-        try:
-            ogr_fielddef = exc_wrap_pointer(OGR_Fld_Create(name_b, field_type))
+    ### Create the fields
+    if create_layer:
+        for i in range(num_fields):
+            field_type, field_subtype, width, precision = field_types[i]
 
-            # subtypes, see: https://gdal.org/development/rfc/rfc50_ogr_field_subtype.html
-            if field_subtype != OFSTNone:
-                OGR_Fld_SetSubType(ogr_fielddef, field_subtype)
+            name_b = fields[i].encode(encoding)
+            try:
+                ogr_fielddef = exc_wrap_pointer(OGR_Fld_Create(name_b, field_type))
 
-            if width:
-                OGR_Fld_SetWidth(ogr_fielddef, width)
+                # subtypes, see: https://gdal.org/development/rfc/rfc50_ogr_field_subtype.html
+                if field_subtype != OFSTNone:
+                    OGR_Fld_SetSubType(ogr_fielddef, field_subtype)
 
-            # TODO: set precision
+                if width:
+                    OGR_Fld_SetWidth(ogr_fielddef, width)
 
-        except:
-            if ogr_fielddef != NULL:
-                OGR_Fld_Destroy(ogr_fielddef)
-                ogr_fielddef = NULL
+                # TODO: set precision
 
-            OGRReleaseDataSource(ogr_dataset)
-            ogr_dataset = NULL
-            raise FieldError(f"Error creating field '{fields[i]}' from field_data") from None
+            except:
+                if ogr_fielddef != NULL:
+                    OGR_Fld_Destroy(ogr_fielddef)
+                    ogr_fielddef = NULL
 
-        try:
-            exc_wrap_int(OGR_L_CreateField(ogr_layer, ogr_fielddef, 1))
+                OGRReleaseDataSource(ogr_dataset)
+                ogr_dataset = NULL
+                raise FieldError(f"Error creating field '{fields[i]}' from field_data") from None
 
-        except:
-            OGRReleaseDataSource(ogr_dataset)
-            ogr_dataset = NULL
-            raise FieldError(f"Error adding field '{fields[i]}' to layer") from None
+            try:
+                exc_wrap_int(OGR_L_CreateField(ogr_layer, ogr_fielddef, 1))
 
-        finally:
-            if ogr_fielddef != NULL:
-                OGR_Fld_Destroy(ogr_fielddef)
+            except:
+                OGRReleaseDataSource(ogr_dataset)
+                ogr_dataset = NULL
+                raise FieldError(f"Error adding field '{fields[i]}' to layer") from None
+
+            finally:
+                if ogr_fielddef != NULL:
+                    OGR_Fld_Destroy(ogr_fielddef)
 
 
     ### Create the features

pyogrio/_ogr.pyx

@@ -100,24 +100,18 @@ def get_gdal_config_option(str name):
     return str_value
 
 
-### Drivers
-# mapping of driver:mode
-# see full list at https://gdal.org/drivers/vector/index.html
-# only for drivers specifically known to operate correctly with pyogrio
-DRIVERS = {
-    # "CSV": "rw",  # TODO: needs geometry conversion method
-    "ESRI Shapefile": "rw",
-    "FlatGeobuf": "rw",
-    "GeoJSON": "rw",
-    "GeoJSONSeq": "rw",
-    "GML": "rw",
-    # "GPX": "rw", # TODO: supports limited geometry types
-    "GPKG": "rw",
-    "OAPIF": "r",
-    "OpenFileGDB": "r",
-    "TopoJSON": "r",
-    # "XLSX": "rw",  # TODO: needs geometry conversion method
-}
+def ogr_driver_supports_write(driver):
+    # exclude drivers known to be unsupported by pyogrio even though they are
+    # supported for write by GDAL
+    if driver in {"CSV", "XLSX"}:
+        return False
+
+
+    # check metadata for driver to see if it supports write
+    if _get_driver_metadata_item(driver, "DCAP_CREATE") == 'YES':
+        return True
+
+    return False
 
 
 def ogr_list_drivers():
@@ -131,9 +125,12 @@ def ogr_list_drivers():
         name_c = <char *>OGR_Dr_GetName(driver)
 
         name = get_string(name_c)
-        # drivers that are not specifically listed have unknown support
-        # this omits any drivers from supported list that are not installed
-        drivers[name] = DRIVERS.get(name, '?')
+
+        if ogr_driver_supports_write(name):
+            drivers[name] = "rw"
+
+        else:
+            drivers[name] = "r"
 
     return drivers
 
@@ -186,7 +183,7 @@ def has_gdal_data():
 
 def get_gdal_data_path():
     """
-    Get the path to the directory GDAL uses to read data files. 
+    Get the path to the directory GDAL uses to read data files.
     """
     cdef const char *path_c = CPLFindFile("gdal", "header.dxf")
     if path_c != NULL: