CODEWITHSUNDEEP
mysqlerlang
asim
asim

Reputation: 553

Erlang and mysql

I have a users table in mysql with userid, username, password etc Using mysql-otp i query like

select * from users where username = ?

Its returns ColumnNames and Rows. Rows are like 

[[38, <<"joe">>, <<"passwordhash">>..]]

Suppose i have a hash to compare

Hash = "passhash".

As its my 3rd day coding in erlang, what i am currently doing/testing is

[[_, _, UserPass, _,..]] = Rows.

Which stores password in UserPass.

Pass = binary_to_list(UserPass).

Which i can then compare like 

Hash == Pass.

Is this approach correct or i am doing it all wrong? There must be a proper way of getting data out of what is supposedly list inside a list.

Upvotes: 0

Views: 112

Answers (1)

7stud
7stud

Reputation: 48599

There must be a proper way of getting data out of what is supposedly list inside a list

The proper way to get at your target data is to use pattern matching to deconstruct whatever type of collection contains your data. Because mysql-otp returns a list of rows matching the query, where each row itself is a list, the data is in the form of a list of lists. Therefore, in order to match a list of lists your pattern also has to be a list of lists.

As its my 3rd day coding in erlang, what i am currently doing/testing is

[[_, _, UserPass, _,..]] = Rows.

Bravo.

If you know mysql-otp will only return one row, or you are only interested in the first row, you could simplify the pattern like this:

[_, _, UserPass, _, ...] = hd(Rows).

hd is shorthand for head, i.e. the head of the list. Or, you could accomplish the same thing by hand like this:

[FirstRow | _Tail] = Rows,
[_, _, UserPass, _, ...] = FirstRow.

=======

Another way to extract the password:

UserPass = lists:nth(3, hd(Rows)).

Upvotes: 1

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