Secondary Indices

【Secondary Indices】

　　EOSIO has the ability to sort tables by up to 16 indices.  A table's struct cannot be modified when it has data in it.

1、添加第二列索引 member 和 getter。

　　The secondary index needs to be numeric field, so a uint64_t was chosen for the age variable

　　

2、Add secondary index to `addresses` table configuration

typedef eosio::multi_index<"people"_n, person, 
indexed_by<"byage"_n, const_mem_fun<person, uint64_t, &person::get_secondary_1>>
  > address_index;

　　1) indexed_by 是一个 struct.

　　2) first parameter set name of index as "byage"

　　3) the second type parameter as a function call operator should extract a const value as an index key.

3、compile & deploy

eosio-cpp -o addressbook.wasm addressbook.cpp --abigen

cleos set contract addressbook /home/ubuntu/contracts/addressbook

4、Test

cleos push action addressbook upsert '["alice", "alice", "liddell", 9, "123 drink me way", "wonderland", "amsterdam"]' -p alice@active

cleos push action addressbook upsert '["bob", "bob", "is a guy", 49, "doesnt exist", "somewhere", "someplace"]' -p bob@active

　　查看一下插入结果，注意--upper 10 是指定上限，即只查看索引值小于10的row.

cleos get table addressbook addressbook people --upper 10 
--key-type i64 
--index 2

　　上面命令会看到结果 

　　

参考：https://developers.eos.io/eosio-home/docs/secondary-indices