How-To Delete from Key-Value Table

Summary

This how-to procedure 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.

Prerequisites

Before you begin, complete the following prerequisites:

• An EOSIO development environment, for details consult the Get Started Guide
• A smart contract named smrtcontract
• A user defined type named person, which defines the data stored in the table
• A kv table type which stores objects of type person, named address_table. The primary index of the kv table is defined based on the person::account_name property.

Refer to the following possible implementation of 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 your 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 possible 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());
}

Next Steps

The following options are available when you complete the procedure:

• 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.