Module hdk::prelude::op

Dht Operational Transforms

These are the operational transformations that can be applied to Holochain data. Every Header produces a set of operations. These operations are each sent to an authority for validation.

Producing Operations

The following is a list of the operations that can be produced by each Header:

• Every Header produces a Op::RegisterAgentActivity and a Op::StoreElement.
• Header::Create also produces a Op::StoreEntry.
• Header::Update also produces a Op::StoreEntry and a Op::RegisterUpdate.
• Header::Delete also produces a Op::RegisterDelete.
• Header::CreateLink also produces a Op::RegisterCreateLink.
• Header::DeleteLink also produces a Op::RegisterDeleteLink.

Authorities

There are three types of authorities in Holochain:

The Header Authority

This set of authorities receives the Op::StoreElement. This is where you can implement your own logic for checking that it is valid to store any of the Header variants according to your own applications rules.

The Entry Authority

This set of authorities receives the Op::StoreEntry. This is where you can implement your own logic for checking that it is valid to store an Entry. You can think of this as the “Create” from the CRUD acronym.

Metadata

The entry authority is also responsible for storing the metadata for each entry. They receive the Op::RegisterUpdate and Op::RegisterDelete. This is where you can implement your own logic for checking that it is valid to update or delete any of the Entry types defined in your application. You can think of this as the “Update” and “Delete” from the CRUD acronym.

They receive the Op::RegisterCreateLink and Op::RegisterDeleteLink. This is where you can implement your own logic for checking that it is valid to place a link on a base Entry.

The Chain Authority

This set of authorities receives the Op::RegisterAgentActivity. This is where you can implement your own logic for checking that it is valid to add a new Header to an agent source chain. You are not validating the individual element but the entire agents source chain.

Author

When authoring a new Header to your source chain, the validation will be run from the perspective of every authority.

A note on metadata for the Header authority.

Technically speaking the Header authority also receives and validates the Op::RegisterUpdate and Op::RegisterDelete but they run the same callback as the Entry authority because it would be inconsistent to have two separate validation outcomes for these ops.

Running Validation

When the fn validate(op: Op) -> ExternResult<ValidateCallbackResult> is called it will be passed the operation variant for the authority that is actually running the validation.

For example the entry authority will be passed the Op::StoreEntry operation.

Enums

EntryCreationHeader

Either a Header::Create or a Header::Update. These headers both create a new instance of an Entry.

Op

The operational transforms that can are applied to Holochain data. Operations beginning with Store are concerned with creating and storing data. Operations beginning with Register are concerned with registering metadata about the data.