feat: Add table_constraints field to Table model (#1755)

* feat: add `table_constraints` field to Table model

* Change `raise` to `return` in __eq__ methods

* Fix __eq__ for ColumnReference

* Add column_references to ForeignKey __eq__

* Add missing coverage

* Update google/cloud/bigquery/table.py

* Update google/cloud/bigquery/table.py

* Update google/cloud/bigquery/table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update google/cloud/bigquery/table.py

* Update google/cloud/bigquery/table.py

* Update google/cloud/bigquery/table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

* Update tests/unit/test_table.py

---------

Co-authored-by: Chalmer Lowe <chalmerlowe@google.com>
Co-authored-by: Chalmer Lowe <chalmer.lowe@gmail.com>

google/cloud/bigquery/table.py

@@ -390,6 +390,7 @@ class Table(_TableBase):
         "view_use_legacy_sql": "view",
         "view_query": "view",
         "require_partition_filter": "requirePartitionFilter",
+        "table_constraints": "tableConstraints",
     }
 
     def __init__(self, table_ref, schema=None) -> None:
@@ -973,6 +974,16 @@ def clone_definition(self) -> Optional["CloneDefinition"]:
             clone_info = CloneDefinition(clone_info)
         return clone_info
 
+    @property
+    def table_constraints(self) -> Optional["TableConstraints"]:
+        """Tables Primary Key and Foreign Key information."""
+        table_constraints = self._properties.get(
+            self._PROPERTY_TO_API_FIELD["table_constraints"]
+        )
+        if table_constraints is not None:
+            table_constraints = TableConstraints.from_api_repr(table_constraints)
+        return table_constraints
+
     @classmethod
     def from_string(cls, full_table_id: str) -> "Table":
         """Construct a table from fully-qualified table ID.
@@ -2958,6 +2969,123 @@ def __repr__(self):
         return "TimePartitioning({})".format(",".join(key_vals))
 
 
+class PrimaryKey:
+    """Represents the primary key constraint on a table's columns.
+
+    Args:
+        columns: The columns that are composed of the primary key constraint.
+    """
+
+    def __init__(self, columns: List[str]):
+        self.columns = columns
+
+    def __eq__(self, other):
+        if not isinstance(other, PrimaryKey):
+            raise TypeError("The value provided is not a BigQuery PrimaryKey.")
+        return self.columns == other.columns
+
+
+class ColumnReference:
+    """The pair of the foreign key column and primary key column.
+
+    Args:
+        referencing_column: The column that composes the foreign key.
+        referenced_column: The column in the primary key that are referenced by the referencingColumn.
+    """
+
+    def __init__(self, referencing_column: str, referenced_column: str):
+        self.referencing_column = referencing_column
+        self.referenced_column = referenced_column
+
+    def __eq__(self, other):
+        if not isinstance(other, ColumnReference):
+            raise TypeError("The value provided is not a BigQuery ColumnReference.")
+        return (
+            self.referencing_column == other.referencing_column
+            and self.referenced_column == other.referenced_column
+        )
+
+
+class ForeignKey:
+    """Represents a foreign key constraint on a table's columns.
+
+    Args:
+        name: Set only if the foreign key constraint is named.
+        referenced_table: The table that holds the primary key and is referenced by this foreign key.
+        column_references: The columns that compose the foreign key.
+    """
+
+    def __init__(
+        self,
+        name: str,
+        referenced_table: TableReference,
+        column_references: List[ColumnReference],
+    ):
+        self.name = name
+        self.referenced_table = referenced_table
+        self.column_references = column_references
+
+    def __eq__(self, other):
+        if not isinstance(other, ForeignKey):
+            raise TypeError("The value provided is not a BigQuery ForeignKey.")
+        return (
+            self.name == other.name
+            and self.referenced_table == other.referenced_table
+            and self.column_references == other.column_references
+        )
+
+    @classmethod
+    def from_api_repr(cls, api_repr: Dict[str, Any]) -> "ForeignKey":
+        """Create an instance from API representation."""
+        return cls(
+            name=api_repr["name"],
+            referenced_table=TableReference.from_api_repr(api_repr["referencedTable"]),
+            column_references=[
+                ColumnReference(
+                    column_reference_resource["referencingColumn"],
+                    column_reference_resource["referencedColumn"],
+                )
+                for column_reference_resource in api_repr["columnReferences"]
+            ],
+        )
+
+
+class TableConstraints:
+    """The TableConstraints defines the primary key and foreign key.
+
+    Args:
+        primary_key:
+            Represents a primary key constraint on a table's columns. Present only if the table
+            has a primary key. The primary key is not enforced.
+        foreign_keys:
+            Present only if the table has a foreign key. The foreign key is not enforced.
+
+    """
+
+    def __init__(
+        self,
+        primary_key: Optional[PrimaryKey],
+        foreign_keys: Optional[List[ForeignKey]],
+    ):
+        self.primary_key = primary_key
+        self.foreign_keys = foreign_keys
+
+    @classmethod
+    def from_api_repr(cls, resource: Dict[str, Any]) -> "TableConstraints":
+        """Create an instance from API representation."""
+        primary_key = None
+        if "primaryKey" in resource:
+            primary_key = PrimaryKey(resource["primaryKey"]["columns"])
+
+        foreign_keys = None
+        if "foreignKeys" in resource:
+            foreign_keys = [
+                ForeignKey.from_api_repr(foreign_key_resource)
+                for foreign_key_resource in resource["foreignKeys"]
+            ]
+        return cls(primary_key, foreign_keys)
+
+
 def _item_to_row(iterator, resource):
     """Convert a JSON row to the native object.