Loosen column length constraints

[orien]

Resolves #145

Context

The default database schema provided by DoubleEntry had small column length limits. These values were specific to the optimisations made on a specific project at Envato. As this project is open source and in use under vastly different use cases, these constraints limit the project effectiveness at satisfying these use cases.

Change

1. Remove the column length constraints from the database migration template. DoubleEntry will operate correctly no matter the size of these columns.

2. Remove the default value for the scope_identifier_max_length, account_identifier_max_length and code_max_length configuration values. The checks will not be performed during account and transfer configuration unless these are options are set.

   DoubleEntry.configure do |config|
     config.code_max_length = 47
     config.account_identifier_max_length = 31
     config.scope_identifier_max_length = 23
   end

MySQL 5.6 schema diff on Rails 5.2 looks like this:

43,44c43,44
<   `account` varchar(31) NOT NULL,
<   `scope` varchar(23) DEFAULT NULL,
---
>   `account` varchar(255) NOT NULL,
>   `scope` varchar(255) DEFAULT NULL,
64,67c64,67
<   `account` varchar(31) NOT NULL,
<   `code` varchar(47) DEFAULT NULL,
<   `partner_account` varchar(31) DEFAULT NULL,
<   `scope` varchar(23) DEFAULT NULL,
---
>   `account` varchar(255) NOT NULL,
>   `code` varchar(255) DEFAULT NULL,
>   `partner_account` varchar(255) DEFAULT NULL,
>   `scope` varchar(255) DEFAULT NULL,
112,113c112,113
<   `key` varchar(48) NOT NULL,
<   `value` varchar(64) NOT NULL,
---
>   `key` varchar(255) NOT NULL,
>   `value` varchar(255) NOT NULL,
130,132c130,132
<   `account` varchar(31) NOT NULL,
<   `scope` varchar(23) DEFAULT NULL,
<   `code` varchar(47) NOT NULL,
---
>   `account` varchar(255) NOT NULL,
>   `scope` varchar(255) DEFAULT NULL,
>   `code` varchar(255) NOT NULL,
136,137c136,137
<   `partner_account` varchar(31) NOT NULL,
<   `partner_scope` varchar(23) DEFAULT NULL,
---
>   `partner_account` varchar(255) NOT NULL,
>   `partner_scope` varchar(255) DEFAULT NULL,

To apply this change a migration similar to the following could be used:

change_column :double_entry_account_balances, :account, :string, limit: 255, null: false
change_column :double_entry_account_balances, :scope,   :string, limit: 255, null: true

change_column :double_entry_line_aggregates, :account,         :string, limit: 255, null: false
change_column :double_entry_line_aggregates, :code,            :string, limit: 255, null: true
change_column :double_entry_line_aggregates, :partner_account, :string, limit: 255, null: true
change_column :double_entry_line_aggregates, :scope,           :string, limit: 255, null: true

change_column :double_entry_line_metadata, :key,   :string, limit: 255, null: false
change_column :double_entry_line_metadata, :value, :string, limit: 255, null: false

change_column :double_entry_lines, :account,         :string, limit: 255, null: false
change_column :double_entry_lines, :scope,           :string, limit: 255, null: true
change_column :double_entry_lines, :code,            :string, limit: 255, null: false
change_column :double_entry_lines, :partner_account, :string, limit: 255, null: false
change_column :double_entry_lines, :partner_scope,   :string, limit: 255, null: true

Engineering teams can choose to apply this change, or apply their own column length constraints specific to their needs.

[scottyp-env]

LGTM, just got a question about the _max_length config values. Are they only there to fail fast so that values that are too long don't get inserted into the database and cause a blow up? Or do they have some other sort of business value? I guess I want to know, is it likely anyone is relying on those being set and they'll be upset if they haven't set those defaults in their config?

[rizalmuthi]

LGTM

[jhilde]

Ironically you did this PR just after we started talking about migrating to uuids.

Any idea when you’ll merge?

[orien]

Hi @jhilde, I was hoping to get this merged this week.

[orien]

just got a question about the _max_length config values. Are they only there to fail fast so that values that are too long don't get inserted into the database and cause a blow up?

@scottyp-env: That's exactly it. Back in Rails 3 when we inserted strings too large for the columns, the values would be silently truncated. So we added these checks.

Now Rails will raise an error when inserting such a string. So these checks are a nice to have as they'll alert us earlier in the development lifecycle, when defining the accounts and transfers rather than when the systems in operating in production.

Actually, now that I think about it the scope_identifier_max_length isn't checked until a transfer is made. There's little value in this check. I'll investigate removing it.

[orien]

There doesn't seem a strong reason for the scope_identifier_max_length check. But I won't remove it here.