query_blocker.rb

The query_blocker extension adds Database#block_queries. Inside the block passed to block_queries, any attempts to execute a query/statement on the database will raise a Sequel::QueryBlocker::BlockedQuery exception.

DB.extension :query_blocker
DB.block_queries do
  ds = DB[:table]          # No exception
  ds = ds.where(column: 1) # No exception
  ds.all                   # Exception raised
end

To handle concurrency, you can pass a :scope option:

# Current Thread
DB.block_queries(scope: :thread){}

# Current Fiber
DB.block_queries(scope: :fiber){}

# Specific Thread
DB.block_queries(scope: Thread.current){}

# Specific Fiber
DB.block_queries(scope: Fiber.current){}

Database#block_queries is useful for blocking queries inside the block. However, there may be cases where you want to allow queries in specific places inside a block_queries block. You can use Database#allow_queries for that:

DB.block_queries do
  DB.allow_queries do
    DB[:table].all           # Query allowed
  end

  DB[:table].all           # Exception raised
end

When mixing block_queries and allow_queries with scopes, the narrowest scope has priority. So if you are blocking with :thread scope, and allowing with :fiber scope, queries in the current fiber will be allowed, but queries in different fibers of the current thread will be blocked.

Note that this should catch all queries executed through the Database instance. Whether it catches queries executed directly on a connection object depends on the adapter in use.

Related module: Sequel::QueryBlocker