How-To Delete from Key-Value Table

Overview

This how-to provides instructions to delete an object from a Key-Value Table (kv table).

Use the method erase defined by the eosio::kv::table type to accomplish this task.

Before you begin

Make sure you have the following prerequisites in place:

• An EOSIO development environment, for details consult the Get Started Guide
• A smart contract named smrtcontract
• A user defined type, struct or class, which defines the data stored in the map, named person
• A kv table data type, struct or class, which inherits eosio::kv::table, and stores objects of type person, named address_table
• A primary index is defined for the kv table for the person::account_name data member

Refer to the following reference implementation for your starting point:

smartcontract.hpp file

struct person {
  eosio::name account_name;
  std::string first_name;
  std::string last_name;
  std::string personal_id;
};

class [[eosio::contract]] smrtcontract : public contract {
    struct [[eosio::table]] address_table : eosio::kv::table<person, "kvaddrbook"_n> {

     index<name> account_name_uidx {
        name{"accname"_n},
        &person::account_name };

     address_table(name contract_name) {
        init(contract_name, account_name_uidx)
     }
  };
  public:
     using contract::contract;
};

Procedure

Complete the following steps to delete a person object from address_table:

1. Create a new action delete, in a smart contract class, which takes as input parameters an account name, a first name, a last name and a personal id.
2. In the delete action access the instance of address_table by declaring a local variable of address_table type.
3. Call the erase method of the address_table and pass to it the primary key for the object which is deleted. If you try to erase an object which is not present in the kv table no error will be raised.

Refer to the following reference implementation to delete a person object from address_table:

smartcontract.hpp file

class [[eosio::contract]] smrtcontract : public contract {
    struct [[eosio::table]] address_table : eosio::kv::table<person, "kvaddrbook"_n> {

     index<name> account_name_uidx {
        name{"accname"_n},
        &person::account_name };

     address_table(name contract_name) {
        init(contract_name, account_name_uidx)
     }
  };
  public:
     using contract::contract;

     // deletes a person based on primary key account_name
     [[eosio::action]]
     void del(eosio::name account_name);

     using del_action = eosio::action_wrapper<"del"_n, &smrtcontract::del>;
};

smartcontract.cpp file

[[eosio::action]]
void smrtcontract::delete(eosio::name account_name) {
  address_table addresses{"kvaddrbook"_n};

  // delete from kv table
  addresses.erase(account_name, get_self());
}

Summary

In conclusion, the above instructions show how to delete an object from a Key-Value Table (kv table).

Next Steps

• Check if the newly inserted person was actually deleted from the table. To accomplish this task, use the exists() function of any index defined for the table.