I'm looking for a very quick way to generate an alphanumeric unique id for a primary key in a table. Efficiently generate a 16-character, alphanumeric string. Dictionaries are used in Python to store key value pairs. The dictionary contains a unique key value as an index and each key represents a particular value. When one or more dictionaries are declared inside another dictionary then it is called a nested dictionary or dictionaries of the dictionary. How you can declare nested dictionaries and access data from them are described. This module provides immutable UUID objects (the UUID class) and the functions uuid1, uuid3, uuid4, uuid5 for generating version 1, 3, 4, and 5 UUIDs as specified in RFC 4122. If all you want is a unique ID, you should probably call uuid1 or uuid4.Note that uuid1 may compromise privacy since it creates a UUID containing the computer’s network address. What is the best way to generate a unique key for the contents of a dictionary. My intention is to store each dictionary in a document store along with a unique id or hash so that I don't have to load the whole dictionary from the store to check if it exists already or not.

Unique keys add a layer of data integrity to an Azure Cosmos container. You create a unique key policy when you create an Azure Cosmos container. With unique keys, you make sure that one or more values within a logical partition is unique. You also can guarantee uniqueness per partition key.

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After you create a container with a unique key policy, the creation of a new or an update of an existing item resulting in a duplicate within a logical partition is prevented, as specified by the unique key constraint. The partition key combined with the unique key guarantees the uniqueness of an item within the scope of the container.

Python Generate A Unique Key

For example, consider an Azure Cosmos container with email address as the unique key constraint and CompanyID as the partition key. When you configure the user's email address with a unique key, each item has a unique email address within a given CompanyID. Two items can't be created with duplicate email addresses and with the same partition key value.

To create items with the same email address, but not the same first name, last name, and email address, add more paths to the unique key policy. Instead of creating a unique key based on the email address only, you also can create a unique key with a combination of the first name, last name, and email address. This key is known as a composite unique key. In this case, each unique combination of the three values within a given CompanyID is allowed.

For example, the container can contain items with the following values, where each item honors the unique key constraint.

CompanyIDFirst nameLast nameEmail address
ContosoGabyDuperre[email protected]
ContosoGabyDuperre[email protected]
FabrikamGabyDuperre[email protected]
FabrikamIvanDuperre[email protected]
FabrkamDuperre[email protected]
Fabrkam[email protected]

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If you attempt to insert another item with the combinations listed in the previous table, you receive an error. The error indicates that the unique key constraint wasn't met. You receive either Resource with specified ID or name already exists or Resource with specified ID, name, or unique index already exists as a return message.

Define a unique key

You can define unique keys only when you create an Azure Cosmos container. A unique key is scoped to a logical partition. In the previous example, if you partition the container based on the ZIP code, you end up with duplicated items in each logical partition. Consider the following properties when you create unique keys:

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  • You can't update an existing container to use a different unique key. In other words, after a container is created with a unique key policy, the policy can't be changed.

  • To set a unique key for an existing container, create a new container with the unique key constraint. Use the appropriate data migration tool to move the data from the existing container to the new container. For SQL containers, use the Data Migration tool to move data. For MongoDB containers, use mongoimport.exe or mongorestore.exe to move data.

  • A unique key policy can have a maximum of 16 path values. For example, the values can be /firstName, /lastName, and /address/zipCode. Each unique key policy can have a maximum of 10 unique key constraints or combinations. The combined paths for each unique index constraint must not exceed 60 bytes. In the previous example, first name, last name, and email address together are one constraint. This constraint uses 3 out of the 16 possible paths.

  • When a container has a unique key policy, Request Unit (RU) charges to create, update, and delete an item are slightly higher.

  • Sparse unique keys are not supported. If some unique path values are missing, they're treated as null values, which take part in the uniqueness constraint. For this reason, there can be only a single item with a null value to satisfy this constraint.

  • Unique key names are case-sensitive. For example, consider a container with the unique key constraint set to /address/zipcode. If your data has a field named ZipCode, Azure Cosmos DB inserts 'null' as the unique key because zipcode isn't the same as ZipCode. Because of this case sensitivity, all other records with ZipCode can't be inserted because the duplicate 'null' violates the unique key constraint.

Next steps

  • Learn more about logical partitions
  • Explore how to define unique keys when creating a container
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