List posts

To list created posts we will be using blogd query blog list-post and blogd query blog get-post command. list-post and get-post subcommand hasn’t been defined yet, so let’s do it now. Query commands (opens new window) from the CLI are handled by query.go.

First we define our proto files, in proto/blog

proto/blog/query.proto

Copy syntax = "proto3"; package example.blog.blog; import "google/api/annotations.proto"; import "cosmos/base/query/v1beta1/pagination.proto"; // this line is used by starport scaffolding # 1 import "blog/post.proto"; option go_package = "github.com/example/blog/x/blog/types"; // Query defines the gRPC querier service. service Query { // this line is used by starport scaffolding # 2 rpc Post(QueryGetPostRequest) returns (QueryGetPostResponse) { option (google.api.http).get = "/example/blog/blog/post/{id}"; } rpc PostAll(QueryAllPostRequest) returns (QueryAllPostResponse) { option (google.api.http).get = "/example/blog/blog/post"; } } // this line is used by starport scaffolding # 3 message QueryGetPostRequest { string id = 1; } message QueryGetPostResponse { Post Post = 1; } message QueryAllPostRequest { cosmos.base.query.v1beta1.PageRequest pagination = 1; } message QueryAllPostResponse { repeated Post Post = 1; cosmos.base.query.v1beta1.PageResponse pagination = 2; }

In our proto file we define the structure of the API endpoint, as well as our request and response structure of the post.

x/blog/client/cli/query.go

Function GetQueryCmd is used for creating a list of query subcommands, it should already be defined. Edit the function to add CmdListPost and CmdShowPost as a subcommand:

Copy cmd.AddCommand(CmdListPost()) cmd.AddCommand(CmdShowPost())

Now let’s define CmdListPost in a new queryPost.go file:

x/blog/client/cli/queryPost.go

Copy package cli import ( "context" "github.com/cosmos/cosmos-sdk/client" "github.com/cosmos/cosmos-sdk/client/flags" "github.com/spf13/cobra" "github.com/example/blog/x/blog/types" ) func CmdListPost() *cobra.Command { cmd := &cobra.Command{ Use: "list-post", Short: "list all post", RunE: func(cmd *cobra.Command, args []string) error { clientCtx, err := client.GetClientTxContext(cmd) if err != nil { return err } pageReq, err := client.ReadPageRequest(cmd.Flags()) if err != nil { return err } queryClient := types.NewQueryClient(clientCtx) params := &types.QueryAllPostRequest{ Pagination: pageReq, } res, err := queryClient.PostAll(context.Background(), params) if err != nil { return err } return clientCtx.PrintProto(res) }, } flags.AddQueryFlagsToCmd(cmd) return cmd } func CmdShowPost() *cobra.Command { cmd := &cobra.Command{ Use: "show-post [id]", Short: "shows a post", Args: cobra.ExactArgs(1), RunE: func(cmd *cobra.Command, args []string) error { clientCtx, err := client.GetClientTxContext(cmd) if err != nil { return err } queryClient := types.NewQueryClient(clientCtx) params := &types.QueryGetPostRequest{ Id: args[0], } res, err := queryClient.Post(context.Background(), params) if err != nil { return err } return clientCtx.PrintProto(res) }, } flags.AddQueryFlagsToCmd(cmd) return cmd }

CmdListPost and CmdShowPost run an ABCI (opens new window) query to fetch the data, unmarshals it back form binary to JSON and returns it to the console. ABCI is an interface between your app and Tendermint (a program responsible for replicating the state across machines). ABCI queries look like paths on a hierarchical filesystem. In our case, the query is custom/blog/list-post. Before we continue, we need to define QueryListPost.

x/blog/types/query.go

Define a QueryListPost that will be used later on to dispatch query requests:

Copy package types const ( QueryGetPost = "get-post" QueryListPost = "list-post" )

x/blog/keeper/query.go

NewQuerier acts as a dispatcher for query functions, it should already be defined. Modify the switch statement to include listPost:

Copy switch path[0] { case types.QueryGetPost: return getPost(ctx, path[1], k, legacyQuerierCdc) case types.QueryListPost: return listPost(ctx, k, legacyQuerierCdc) default:

Now let’s define listPost:

x/blog/keeper/query_post.go

Create a new file query_post.go in the keeper/ directory

Make sure to add the codec to the previous import and add the listPost and getPost function in a new file called query_post.go in our keeper.

Copy package keeper import ( "github.com/cosmos/cosmos-sdk/codec" sdk "github.com/cosmos/cosmos-sdk/types" sdkerrors "github.com/cosmos/cosmos-sdk/types/errors" ) func listPost(ctx sdk.Context, keeper Keeper, legacyQuerierCdc *codec.LegacyAmino) ([]byte, error) { msgs := keeper.GetAllPost(ctx) bz, err := codec.MarshalJSONIndent(legacyQuerierCdc, msgs) if err != nil { return nil, sdkerrors.Wrap(sdkerrors.ErrJSONMarshal, err.Error()) } return bz, nil } func getPost(ctx sdk.Context, id string, keeper Keeper, legacyQuerierCdc *codec.LegacyAmino) ([]byte, error) { msg := keeper.GetPost(ctx, id) bz, err := codec.MarshalJSONIndent(legacyQuerierCdc, msg) if err != nil { return nil, sdkerrors.Wrap(sdkerrors.ErrJSONMarshal, err.Error()) } return bz, nil }

In the keeper we define also the grpc of our queryPost function.

x/block/keeper/grpc_query_post.go

Copy package keeper import ( "context" "github.com/cosmos/cosmos-sdk/store/prefix" sdk "github.com/cosmos/cosmos-sdk/types" "github.com/cosmos/cosmos-sdk/types/query" "github.com/example/blog/x/blog/types" "google.golang.org/grpc/codes" "google.golang.org/grpc/status" ) func (k Keeper) PostAll(c context.Context, req *types.QueryAllPostRequest) (*types.QueryAllPostResponse, error) { if req == nil { return nil, status.Error(codes.InvalidArgument, "invalid request") } var posts []*types.Post ctx := sdk.UnwrapSDKContext(c) store := ctx.KVStore(k.storeKey) postStore := prefix.NewStore(store, types.KeyPrefix(types.PostKey)) pageRes, err := query.Paginate(postStore, req.Pagination, func(key []byte, value []byte) error { var post types.Post if err := k.cdc.UnmarshalBinaryBare(value, &post); err != nil { return err } posts = append(posts, &post) return nil }) if err != nil { return nil, status.Error(codes.Internal, err.Error()) } return &types.QueryAllPostResponse{Post: posts, Pagination: pageRes}, nil } func (k Keeper) Post(c context.Context, req *types.QueryGetPostRequest) (*types.QueryGetPostResponse, error) { if req == nil { return nil, status.Error(codes.InvalidArgument, "invalid request") } var post types.Post ctx := sdk.UnwrapSDKContext(c) store := prefix.NewStore(ctx.KVStore(k.storeKey), types.KeyPrefix(types.PostKey)) k.cdc.MustUnmarshalBinaryBare(store.Get(types.KeyPrefix(types.PostKey + req.Id)), &post) return &types.QueryGetPostResponse{Post: &post}, nil }

We add the grpc query handler to our module on

x/blog/module.go

Let's make sure to import context and add the RegisterGRPCGatewayRoutes

Copy import ( "context" // ... other imports ) Copy func (AppModuleBasic) RegisterGRPCGatewayRoutes(clientCtx client.Context, mux *runtime.ServeMux) { types.RegisterQueryHandlerClient(context.Background(), mux, types.NewQueryClient(clientCtx)) }

This function uses a prefix iterator to loop through all the keys with a given prefix (in our case PostPrefix is "post-"). We’re getting values by key with store.Get and appending them to postList. Finally, we unmarshal bytes back to JSON and return the result to the console.

Now let’s see how it works. Run the following command to recompile your app, clear the data and relaunch the chain:

Copy starport serve

After the app has launched, open a different terminal window and create a post:

Copy blogd tx blog create-post 'Hello!' 'This is my first blog post.' --from=user1

Now run the query to see the post:

Copy blogd query blog list-post Copy [ { "creator": "cosmos1mc6leyjdwd9ygxeqdnvtsh7ks3knptjf3s5lf9", "title": "Hello!", "body": "This is my first blog post.", "id": "30808a80-799d-475c-9f5d-b382ea24d79c" } ]

That’s a newly created post along with your address and a unique ID. Try creating more posts and see the output.

We can also make ABCI (opens new window) queries from the browser:

Copy http://localhost:26657/abci_query?path="custom/blog/list-post"

The result of this query is a base64 encoded string inside result.response.value. You can decode it using a browser’s built in JavaScript console: atob("WwogIHsKICAgICJjcmV...").

Errors

null

Copy blogd q blog list-post null

This is actually not an error, but may be a bit confusing. If you've added a post and immediately issued list-post subcommand, you may get a null. This happens, because it takes several seconds to process the block. After a couple of seconds you should be able to see output of list-post subcommand.