Show a post

In this chapter, you will implement a feature in your blogging application that enables users to retrieve individual blog posts by their unique ID. This ID is assigned to each blog post when it is created and stored on the blockchain. By adding this querying functionality, users will be able to easily retrieve specific blog posts by specifying their ID.

Show post

Let's implement the ShowPost keeper method that will be called when a user makes a query to the blockchain application, specifying the ID of the desired post.

x/blog/keeper/query_show_post.go

package keeper

import (
    "context"

    "blog/x/blog/types"

    sdk "github.com/cosmos/cosmos-sdk/types"
    sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
    "google.golang.org/grpc/codes"
    "google.golang.org/grpc/status"
)

func (k Keeper) ShowPost(goCtx context.Context, req *types.QueryShowPostRequest) (*types.QueryShowPostResponse, error) {
    if req == nil {
        return nil, status.Error(codes.InvalidArgument, "invalid request")
    }

    ctx := sdk.UnwrapSDKContext(goCtx)
    post, found := k.GetPost(ctx, req.Id)
    if !found {
        return nil, sdkerrors.ErrKeyNotFound
    }

    return &types.QueryShowPostResponse{Post: post}, nil
}

ShowPost is a function for retrieving a single post object from the blockchain's state. It takes in two arguments: a context.Context object called goCtx and a pointer to a types.QueryShowPostRequest object called req. It returns a pointer to a types.QueryShowPostResponse object and an error.

The function first checks if the req argument is nil. If it is, it returns an error with the code InvalidArgument and the message "invalid request" using the status.Error function from the google.golang.org/grpc/status package.

If the req argument is not nil, the function unwraps the sdk.Context object from the context.Context object using the sdk.UnwrapSDKContext function. It then retrieves a post object with the specified Id from the blockchain's state using the GetPost function, and checks if the post was found by checking the value of the found boolean variable. If the post was not found, it returns an error with the type sdkerrors.ErrKeyNotFound.

If the post was found, the function creates a new types.QueryShowPostResponse object with the retrieved post object as a field, and returns a pointer to this object and a nil error.

Modify QueryShowPostResponse

Include the option [(gogoproto.nullable) = false] in the post field in the QueryShowPostResponse message to generate the field without a pointer.

proto/blog/blog/query.proto

message QueryShowPostResponse {
  Post post = 1 [(gogoproto.nullable) = false];
}

Run the command to generate Go files from proto:

ignite generate proto-go