Add upsert docs

mkdocs/docs/api.md

@@ -474,6 +474,71 @@ lat: [[48.864716],[52.371807],[53.11254],[37.773972]]
 long: [[2.349014],[4.896029],[6.0989],[-122.431297]]
 ```
 
+### Upsert
+
+PyIceberg supports upsert operations, meaning that it is able to merge an Arrow table into an Iceberg table. Rows are considered the same based on the [identifier field](https://iceberg.apache.org/spec/?column-projection#identifier-field-ids). If a row is already in the table, it will update that row. If a row cannot be found, it will insert that new row.
+
+Consider the following table, with some data:
+
+```python
+from pyiceberg.schema import Schema
+from pyiceberg.types import IntegerType, NestedField, StringType
+
+import pyarrow as pa
+
+schema = Schema(
+    NestedField(1, "city", StringType(), required=True),
+    NestedField(2, "inhabitants", IntegerType(), required=True),
+    # Mark City as the identifier field, also known as the primary-key
+    identifier_field_ids=[1]
+)
+
+tbl = catalog.create_table("default.cities", schema=schema)
+
+arrow_schema = pa.schema(
+    [
+        pa.field("city", pa.string(), nullable=False),
+        pa.field("inhabitants", pa.int32(), nullable=False),
+    ]
+)
+
+# Write some data
+df = pa.Table.from_pylist(
+    [
+        {"city": "Amsterdam", "inhabitants": 921402},
+        {"city": "San Francisco", "inhabitants": 808988},
+        {"city": "Drachten", "inhabitants": 45019},
+        {"city": "Paris", "inhabitants": 2103000},
+    ],
+    schema=arrow_schema
+)
+tbl.append(df)
+```
+
+Next, we'll upsert a table into the Iceberg table:
+
+```python
+df = pa.Table.from_pylist(
+    [
+        # Will be updated, the inhabitants has been updated
+        {"city": "Drachten", "inhabitants": 45505},
+
+        # New row, will be inserted
+        {"city": "Berlin", "inhabitants": 3432000},
+
+        # Ignored, already exists in the table
+        {"city": "Paris", "inhabitants": 2103000},
+    ],
+    schema=arrow_schema
+)
+upd = tbl.upsert(df)
+
+assert upd.rows_updated == 1
+assert upd.rows_inserted == 1
+```
+
+PyIceberg will automatically detect which rows need to be updated, inserted or can simply be ignored.
+
 ## Inspecting tables
 
 To explore the table metadata, tables can be inspected.

pyiceberg/table/__init__.py

@@ -1109,7 +1109,7 @@ def name_mapping(self) -> Optional[NameMapping]:
     def upsert(
         self,
         df: pa.Table,
-        join_cols: list[str],
+        join_cols: Optional[List[str]] = None,
         when_matched_update_all: bool = True,
         when_not_matched_insert_all: bool = True,
         case_sensitive: bool = True,
@@ -1119,11 +1119,13 @@ def upsert(
         Args:
 
             df: The input dataframe to upsert with the table's data.
-            join_cols: The columns to join on. These are essentially analogous to primary keys
+            join_cols: Columns to join on, if not provided, it will use the identifier-field-ids.
             when_matched_update_all: Bool indicating to update rows that are matched but require an update due to a value in a non-key column changing
             when_not_matched_insert_all: Bool indicating new rows to be inserted that do not match any existing rows in the table
             case_sensitive: Bool indicating if the match should be case-sensitive
 
+            To learn more about the identifier-field-ids: https://iceberg.apache.org/spec/#identifier-field-ids
+
                 Example Use Cases:
                     Case 1: Both Parameters = True (Full Upsert)
                     Existing row found → Update it
@@ -1148,6 +1150,15 @@ def upsert(
         """
         from pyiceberg.table import upsert_util
 
+        if join_cols is None:
+            join_cols = []
+            for field_id in self.schema().identifier_field_ids:
+                col = self.schema().find_column_name(field_id)
+                if col is not None:
+                    join_cols.append(col)
+                else:
+                    raise ValueError(f"Field-ID could not be found: {join_cols}")
+
         if not when_matched_update_all and not when_not_matched_insert_all:
             raise ValueError("no upsert options selected...exiting")
 

tests/table/test_upsert.py

@@ -16,13 +16,16 @@
 # under the License.
 from pathlib import PosixPath
 
+import pyarrow as pa
 import pytest
 from datafusion import SessionContext
 from pyarrow import Table as pa_table
 
 from pyiceberg.catalog import Catalog
 from pyiceberg.exceptions import NoSuchTableError
+from pyiceberg.schema import Schema
 from pyiceberg.table import UpsertResult
+from pyiceberg.types import IntegerType, NestedField, StringType
 from tests.catalog.test_base import InMemoryCatalog, Table
 
 
@@ -314,3 +317,52 @@ def test_key_cols_misaligned(catalog: Catalog) -> None:
 
     with pytest.raises(Exception, match=r"""Field ".*" does not exist in schema"""):
         table.upsert(df=df_src, join_cols=["order_id"])
+
+
+def test_upsert_with_identifier_fields(catalog: Catalog) -> None:
+    identifier = "default.test_upsert_with_identifier_fields"
+    _drop_table(catalog, identifier)
+
+    schema = Schema(
+        NestedField(1, "city", StringType(), required=True),
+        NestedField(2, "inhabitants", IntegerType(), required=True),
+        # Mark City as the identifier field, also known as the primary-key
+        identifier_field_ids=[1],
+    )
+
+    tbl = catalog.create_table(identifier, schema=schema)
+
+    arrow_schema = pa.schema(
+        [
+            pa.field("city", pa.string(), nullable=False),
+            pa.field("inhabitants", pa.int32(), nullable=False),
+        ]
+    )
+
+    # Write some data
+    df = pa.Table.from_pylist(
+        [
+            {"city": "Amsterdam", "inhabitants": 921402},
+            {"city": "San Francisco", "inhabitants": 808988},
+            {"city": "Drachten", "inhabitants": 45019},
+            {"city": "Paris", "inhabitants": 2103000},
+        ],
+        schema=arrow_schema,
+    )
+    tbl.append(df)
+
+    df = pa.Table.from_pylist(
+        [
+            # Will be updated, the inhabitants has been updated
+            {"city": "Drachten", "inhabitants": 45505},
+            # New row, will be inserted
+            {"city": "Berlin", "inhabitants": 3432000},
+            # Ignored, already exists in the table
+            {"city": "Paris", "inhabitants": 2103000},
+        ],
+        schema=arrow_schema,
+    )
+    upd = tbl.upsert(df)
+
+    assert upd.rows_updated == 1
+    assert upd.rows_inserted == 1