How to insert data into a multi-index table

Overview

This guide provides instructions to insert data into a multi-index table.

Reference

See the following code reference:

• The multi-index class.
• The multi-index::find(...) method.
• The multi-index::emplace(...) method.

Before you begin

Make sure you have the following prerequisites in place:

• An Antelope development environment, for details consult the Documentation Portal.
• A multi-index testab table instance which stores user objects indexed by the primary key which is of type eosio::name. Consult the section How to instantiate a multi-index table to learn how to set it up.

Procedure

Complete the following steps to insert an user object in the testtab multi-index table:

1. Verify If The User Already Exists

Use of the multi-index table iterator to find out if the user object already exists. The targeted user is searched based on its account name.

[[eosio::action]] void multi_index_example::set( name user ) {
  // check if the user already exists
  auto itr = testtab.find(user.value);
}

2. Insert The User If Not Found In Table

Use the emplace method to make the insertion if the user object is not already in the multi-index table. Otherwise print an informational message.

[[eosio::action]] void multi_index_example::set( name user ) {
  // check if the user already exists
  auto itr = testtab.find(user.value);

+  if ( itr == testtab.end() ) {
+    testtab.emplace( _self, [&]( auto& u ) {
+      u.test_primary = user;
+      u.secondary = "second"_n;
+      u.datum = 0;
+    });
+  }
+  else {
+    printf("User already exists.");
+  }
}

[[info | Full example location]] | A full example project demonstrating the instantiation and usage of multi-index table can be found here.

Summary

In conclusion, the above instructions show how to insert data in a multi-index table.

Next Steps

• You can iterate and retrieve newly inserted data from the multi-index table.