get_field

Retrieve a single or multiple fields from a single record selected by its primary key.

retrieved_item: Optional[Any] = table_client.get_field(
    key_value=str, field_path=str, 
    query_kwargs=Optional[dict],
    data_validation=bool = True
)

Parameters#

Property name	Required	Accepted types	Default	Description
key_value	YES	Any	-	The path expression to target the attribute to set/update in your record. See Field path selectors
field_path	YES	str	-	The path expression to target the attribute to set/update in your record. See Field path selectors
query_kwargs	NO	dict	None	Used to pass data to populate a field_path that contains keys. See example below :
data_validation	NO	bool	True	Whether data validation from your table model should be applied on the retrieved data.

Availability#

Table	Available
DynamoDBBasicTable	✅
DynamoDBCachingTable	✅
ExternalDynamoDBApiBasicTable	✅
ExternalDynamoDBApiCachingTable	✅

Single field retrieving#

Queried record#

{
  "userId": "x42",
  "username": "Robinson",
  "friends": {
    "b242": {
      "relationshipStatus": "superFriend"
    },
    "b59O": {
      "relationshipStatus": "lover"
    },
    "b112": {
      "relationshipStatus": "businessPartner"
    }
  }
}

Code#

from StructNoSQL import TableDataModel, DynamoDBBasicTable, PrimaryIndex, BaseField, MapModel
from typing import Dict, Optional


class UsersTableModel(TableDataModel):
    userId = BaseField(field_type=str, required=True)
    class FriendModel(MapModel):
        relationshipStatus = BaseField(field_type=str, required=False)
    friends = BaseField(field_type=Dict[str, FriendModel], key_name='friendId', required=False)


class UsersTable(DynamoDBBasicTable):
    def __init__(self):
        primary_index = PrimaryIndex(hash_key_name='userId', hash_key_variable_python_type=str)
        super().__init__(
            table_name='accounts-data', region_name='eu-west-2',
            data_model=UsersTableModel(), primary_index=primary_index,
            auto_create_table=True
        )


table_client = UsersTable()

requested_friend_id = 'b112'
# Typing the response_data with Optional or with str, is purely optional.
# Use it if you consider that it will make your code clearer.
response_data: Optional[str] = table_client.get_field(
    key_value='x42',
    field_path='friends.{{friendId}}.relationshipStatus',
    query_kwargs={'friendId': requested_friend_id},
)
if response_data is None:
    print(f"Status or friend with id {requested_friend_id} not found.")
else:
    print(f"Relationship status with {requested_friend_id} is {response_data}")

Output#

Relationship status with b112 is businessPartner

Multi fields selectors#

If you need to access multiple items that share the same location, you can use a multi-selector. In the field_path specify the attributes you want to retrieved by enclosing them in brackets and with a comma separating each attribute. For example : myItem.(attribute1, attribute2, attribute3)

tip

A single database request will be constructed and send to retrieve your multiple attributes. It is then more efficient to use multi selectors or the get_multiple_fields operation as much as you can, instead of sending multiple operations to your database to retrieve the data you need.

You cannot use a multi-selector to get multiple fields that are not in the same location. For that use case, you need the get_multiple_fields operation.

Queried record#

{
  "userId": "x42",
  "username": "Robinson",
  "friends": {
    "b112": {
      "name": "Malo",
      "profession": "electrical engineer",
      "score": 100
    }
  }
}

Code#

from StructNoSQL import TableDataModel, DynamoDBBasicTable, PrimaryIndex, BaseField, MapModel
from typing import Dict, Optional


class UsersTableModel(TableDataModel):
    userId = BaseField(field_type=str, required=True)
    class FriendModel(MapModel):
        name = BaseField(field_type=str, required=False)
        profession = BaseField(field_type=str, required=False)
        score = BaseField(field_type=int, required=False)
    friends = BaseField(field_type=Dict[str, FriendModel], key_name='friendId', required=False)


class UsersTable(DynamoDBBasicTable):
    def __init__(self):
        primary_index = PrimaryIndex(hash_key_name='userId', hash_key_variable_python_type=str)
        super().__init__(
            table_name='accounts-data', region_name='eu-west-2',
            data_model=UsersTableModel, primary_index=primary_index,
            auto_create_table=True
        )


table_client = UsersTable()

requested_friend_id = 'b112'
response_data: Optional[dict] = table_client.get_field(
    key_value='x42',
    field_path='friends.{{friendId}}.(name, profession, score)',
    query_kwargs={'friendId': requested_friend_id}
)
print(response_data)

Output#

{'name': 'Malo', 'profession': 'electrical engineer', 'score': 100}