SELECT value from "column" for which row is retrieved

Question

Problem Say I have a table with the following structure.

int value | asset tokenType
4    | 0 bitcoin 
7    | 0 altcoin. 

Now I also have this function where I pass in an asset and i want to retrieve the value. Pretend I pass in bitcoin as coinType.

I know I can say

auto iterator = table.find(coinType.symbol.raw());

and iterator will be that row or be at the end if nothing is found.

HOWEVER, what I am trying to accomplish is selecting this 7. Something like "SELECT But how can I SELECT value ( which would be 7), like I would in sql. ( I know this isn't sql btw )

But this is my table structure

TABLE items{
   int id;
   asset value ;
   asset tokenType;
   std:: string note;
  //Primary key is symbol of tokenType
  uint64_t primary_key() const {return tokenType.symbol.raw();}

   };

Answer 1

Ok, now that I read your question again I see that I maybe misunderstood the question.

auto iterator = table.find(coinType.symbol.raw());

returns a pointer to the dataset with the specific value.

If you want to access members of the row behind the pointer you have to use the

arrow-operator "->"

so

int test_access_member = iterator->id;

will let you access the value.

You should take a look at C/C++ pointers and references.

Answer 2

At first, there's nothing like "SELECT"-Statements

If you want to find by rows by values of a certain column you need to add more indexes. In your case:

long secondary_key() const {return id;}
....
typedef eosio::multi_index<"assets"_n, asset, eosio::indexed_by<"id"_n, eosio::const_mem_fun<asset, long, &asset::secondary_key>>> assetstable;

Now you can use find on the id-column if you do

auto id_index = table.get_index<N(byid)>();
auto row = id_index.find(id);

But note that you have to use at minimum a 64-bit type as index-type.