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Store and Fetch Data

Saving to storage is a way to save state on the blockchain. This opens up a lot more possibilities for richer blockchain apps.

There are two ways to save data to the blockchain:

  • dyson/sendMsgCreateStorage - create storage at a new index
  • dyson/sendMsgUpdateStorage - update existing storage

There are three ways to read from storage

  • dyson/QueryStorage - Retreave a single storage at the index
  • dyson/QueryPrefixStorage - List all storage with an index that starts with a prefix
  • dyson/QueryStorageAll - List all storage on the chain
Access Control

This line prevents anyone from running your function except you. You will see this used in the examples below.

assert SCRIPT_ADDRESS == CALLER, "not allowed"

Create​

This code defines a function called create that takes in three parameters: index, data, and force. The function first checks if the value of SCRIPT_ADDRESS is equal to the value of CALLER. If it is not equal, the function raises AssertionError('not allowed'). If the assertion passes, the function calls the _chain function from the dys module. If force=True it will never raise an exception and will always write to the index regardless of any existing data or not.

from dys import _chain, SCRIPT_ADDRESS, CALLER


def create(index: str, data: str, force: bool):
    assert SCRIPT_ADDRESS == CALLER, "not allowed"
    return _chain(
        "dyson/sendMsgCreateStorage",
        creator=SCRIPT_ADDRESS,
        index=SCRIPT_ADDRESS + "/" + index,
        data=data,
        force=force,
    )

Retrieve​

This example defines two functions, get and list, that interact with a storage system using the _chain function.

The get function takes in a parameter index which is a string. It then constructs a storage query by calling _chain with the dyson/QueryStorage method and passing in the index with the SCRIPT_ADDRESS concatenated to it.

See also: https://dys-api.dysonprotocol.com/#/Query/DysonStorage

def get(index: str):
    return _chain(
        "dyson/QueryStorage",
        index=SCRIPT_ADDRESS + "/" + index,
    )

The list function takes in a parameter prefix which is also a string. It constructs a storage query by calling _chain with the "dyson/QueryPrefixStorage" method and passing in the prefix with the SCRIPT_ADDRESS concatenated to it.

See also: https://dys-api.dysonprotocol.com/#/Query/DysonPrefixStorage

def list(prefex: str):
    return _chain("dyson/QueryPrefixStorage", prefix=SCRIPT_ADDRESS + "/" + prefex)

Both of these example functions return the result of the _chain function call.

Update​

This will update an existing Storage object at the given index or will return an error if it is not there.

If force=True it will never raise an exception and will always write to the index.

def update(index: str, data: str, force: bool):
    assert SCRIPT_ADDRESS == CALLER, "not allowed"
    return _chain(
        "dyson/sendMsgUpdateStorage",
        creator=SCRIPT_ADDRESS,
        index=SCRIPT_ADDRESS + "/" + index,
        data=data,
        force=force,  # set to True to always write to this index
    )

Delete​

This will delete an existing Storage object at the given index or will return an error if it is not there.

def delete(index: str):
    assert SCRIPT_ADDRESS == CALLER, "not allowed"
    return _chain(
        "dyson/sendMsgDeleteStorage",
        creator=SCRIPT_ADDRESS,
        index=SCRIPT_ADDRESS + "/" + index,
    )