How to access data inside multi-index table when using 2D vector / 2D array?

Question

What is going on? :D I write data, but cannot find it after I write it.

The following code successfully emplaces the row into the multi-index table:

See specifically the vector<vector <structnamex::plot >> map parameter which is what I am dubious about.

ACTION structnamex::createland(name land_id, string land_name, uint8_t x_size,
uint8_t y_size, vector<vector<structnamex::plot>> map) {

        require_auth( get_self() );
    
        lands_index _southlands( get_self(), get_self().value );
     
        uint8_t find_y = map.size();
        uint8_t find_x;
        if(find_y > 0)
        { find_x = map[0].size(); }
    
        check((x_size == find_x), "x_size value does not match x value in map[y][x]");
        check((y_size == find_y), "y_size value does not match y value in map[y][x]");
        check((x_size > 0), "x_size value must be greater than 0");
        check((y_size > 0), "y_size value must be greater than 0");
    
        //check all x values
        for (int i = 0; i < y_size; i++) {
             check((map[i].size() == x_size), "x_size value does not match x value in map[y][x] in later rows");
        }
    
        print("X val: ", find_x, " -- Y val: ", find_y);
        _southlands.emplace( get_self(), [&]( auto& land_row ) {
            land_row.land_id    = land_id;
            land_row.land_name  = land_name;
            land_row.x_size     = x_size;
            land_row.y_size     = y_size;
            land_row.map        = map;
    
            print("-- data emplaced!");
        });
    }

In the header file we have the structures declared as follows

    // ... inside contract declaration ...

    /// the plot struct from the header file is as follows:
    struct plot {
       name owner;
       uint16_t type;

       EOSLIB_SERIALIZE(plot, (owner)(type));
    };
    
    // the multi-index table is as follows
    TABLE lands {
    name          land_id;
    string        land_name;
    uint8_t       x_size;
    uint8_t       y_size;
    vector<vector<structnamex::plot>>  map;

    auto primary_key() const { return land_id.value; };

    };

I write this data in EOS Studio:

land_id: funland
land_name: Fun Land Central
x_size: 2
y_size: 2

map: [[{"owner": "useraccount","type": 20},{"owner": "useraccount","type": 20}],
[{"owner": "useraccount","type": 20},{"owner": "useraccount","type": 20}]]

According to the console output, it successfully writes. If I try to write this data again, it fails, saying that index already exists.

This data will not display in EOS Studio when you refresh the multi-index table. It produces the error, " FC Exception encountered while processing chain.get_table_rows "

Even though it wont display in EOS Studio, I use some smart contract code to see if it's there:

ACTION structnamex::testprint(name land_id, uint8_t x, uint8_t y) {

    lands_index _southlands( get_self(), get_self().value );

    auto itr = _southlands.find(land_id.value);

    if(itr != _southlands.end()) {
        print("found!");
    }
    else {
        print("land not found"); }
};

The function when run with the following submits the transaction without error, but the console gives no output.

land_id:  funland
x: 1
y: 1

Answer 1

A couple of comments:

1. about when you try to write again, it fails, saying that index already exists; the code just uses tblIndex.emplace() method to populate the data no matter what, actually he should use tblndex.modify() when the data exists.

        lands_index _southlands( get_self(), get_self().value );

        auto iter = lands_index.find(land_id.value); 
        if (iter == lands_index.end()) 
        { 
            lands_index.emplace(get_self(), [&](auto &row) { 
            row.land_id    = land_id;
                        ...assign other fields...
                    });
        } 
        else 
        { 
            lands_index.modify(iter,get_self(), [&]( auto& row ) { 
                        ...assign other fields...
                    }); 
        } 

2. Also try to use typedef to deal with vector<vector>

i.e typedef 
    vector<structnamex::plot> vec_plot;
replace
    vector<vector<structnamex::plot>> with vector<vec_plot>