Database might be busy when close is called

[kanoshin]

Hello,

according to SQLite documentation sqlite3_close might return SQLITE_BUSY (http://www.sqlite.org/c3ref/close.html). It usually means that there are not finalized statements.

I see that this plugin don't handle such scenario, it might lead to creation of new database connections when sqlite3_open will be called later, right?

From http://sqlite.1065341.n5.nabble.com/handling-sqlite3-close-SQLITE-BUSY-td35617.html:

You can force connection closing in case
of SQLITE_BUSY result by forcible finalizing of all statements. Use
http://www.sqlite.org/c3ref/next_stmt.html for iterating all
statements and sqlite3_finalize on each of them. After that
sqlite3_close should complete successfully.

[kanoshin]

@brodybits thank you.
I think this might fix errors that sometimes occur right after app navigates to different page or recreates database connection:
{\"result\":{\"code\":5,\"sqliteCode\":1,\"message\":\"cannot start a transaction within a transaction\"}}
{\"result\":{\"code\":0,\"sqliteCode\":14,\"message\":\"unable to open database file\"}}
{\"result\":{\"code\":0,\"sqliteCode\":5,\"message\":\"sqlite3_step failure: database is locked\"}}

[brodycj]

This looks like yet another problem with using "standard" Web SQL transaction calls (database.transaction() and database.readTransaction()) together with multi-page apps, possibly related to #666. It would be better to use database.executeSql() and database.sqlBatch() calls as documented instead.

The database.transaction() and database.readTransaction() calls are deprecated and scheduled to be removed from this plugin version ref: #720, #690

An additional suggestion is to consider using https://github.com/brodybits/sql-promise-helper to get a nice, clean Promise-based API, also working on the Browser platform today.