cosmos-sdk/docs/sdk/sdk-by-examples/simple-governance/app-structure.md

Application structure

Now, that we have built all the pieces we need, it is time to integrate them into the application. Let us exit the /x director go back at the root of the SDK directory.

// At root level of directory
cd app

We are ready to create our simple governance application!

Note: You can check the full file (with comments!) here

The app.go file is the main file that defines your application. In it, you will declare all the modules you need, their keepers, handlers, stores, etc. Let us take a look at each section of this file to see how the application is constructed.

Secondly, we need to define the name of our application.

const (
    appName = "SimpleGovApp"
)

Then, let us define the structure of our application.

// Extended ABCI application
type SimpleGovApp struct {
    *bam.BaseApp
    cdc *wire.Codec

    // keys to access the substores
    capKeyMainStore      *sdk.KVStoreKey
    capKeyAccountStore   *sdk.KVStoreKey
    capKeyStakingStore   *sdk.KVStoreKey
    capKeySimpleGovStore *sdk.KVStoreKey

    // keepers
    feeCollectionKeeper auth.FeeCollectionKeeper
    coinKeeper          bank.Keeper
    stakeKeeper         simplestake.Keeper
    simpleGovKeeper     simpleGov.Keeper

    // Manage getting and setting accounts
    accountMapper auth.AccountMapper
}

• Each application builds on top of the BaseApp template, hence the pointer.
• cdc is the codec used in our application.
• Then come the keys to the stores we need in our application. For our simple governance app, we need 3 stores + the main store.
• Then come the keepers and mappers.

Let us do a quick reminder so that it is clear why we need these stores and keepers. Our application is primarily based on the simple_governance module. However, we have established in section Keepers for our app that our module needs access to two other modules: the bank module and the stake module. We also need the auth module for basic account functionalities. Finally, we need access to the main multistore to declare the stores of each of the module we use.