See lib/example_squeal.rb for the example squeal.
To run standalone, simply make your data squeal thusly:
where the squeal script includes a
Object#targetverifies there is a variable in scope with the same name as the
table_namebeing targetted, it must be a
Hashand must have an
- Block to
Object#assignnot required, infers value from source scope
- A block returning
nilas the value to
Object#assign, rather than inferring value from source scope
Squealer is for standalone operation. DO NOT use it directly from within your Ruby application. To make the DSL easy to use, we alter some core types:
FalseClass#to_i- You'll be storing booleans as a
tinyint(1), or similar.
Hash#method_missing- You prefer dot notation. JSON uses dot notation. You are importing from a data store which represents collections as arrays of hashmaps. Dot notation for navigating those collections is convenient. If you use a field name that happens to be a method on Hash you will have to use index notation. (e.g.
kitten.toysis good, however
kitten.freezeis not good. Use
NilClass#each- As you are importing from schemaless repositories and you may be trying to iterate on fields that contain embedded collections, if a specific parent does not contain one of those child collections, the driver will be returning
nilas the value for that field. Having
for a nil is convenient, semantically correct in this context, and removes the need for many
nilchecks in the block you provide to
#assign"keywords" are provided for convenience
Time#to_s- As you are exporting to a SQL database, we represent your timestamp in a format that it will parse unequivocally (MongoDB stores all temporal data as a timestamp)
TrueClass#to_i- You'll be storing booleans as a
tinyint(1), or similar.
Squealer doesn't use your application classes. It doesn't use your ActiveRecord models. It doesn't use mongoid (as awesome as that is), or mongomapper. It's an ETL tool. It could even be called a HRM (Hashmap-Relational-Mapper), but only in hushed tones in the corner boothes of dark pubs. It directly uses the Ruby driver for MongoDB and the Ruby driver for mySQL.
For now, this is specifically for MongoDB exporting to mySQL.
Since version 1.1, the primary key value is inferred from the source document
_id field based on the
table_name argument matching the name of a variable holding the source document,
row_id is no longer a parameter on
Object#target. It will be invalid in version 1.3 and above.
The target SQL database must have no foreign keys (because it can't rely on the primary key values and referential integrity is the responsibility of the source data store or the application that uses it).
The target SQL database must use a primary key of
char(24). For now, we've assumed that column name is
id. Each record's
id value will get the source document
It is assumed the target data will be quite denormalized - particularly that the hierarchy keys for embedded documents are flattened. This means that a document from
office.room.box will be exported to a record containing the
room and the
It is assumed no indexes are present in the target database table (performance drag). You may want to create indexes for pulling data out of the database Squealer exports to. Run a SQL DDL script on your mySQL database after squealing to add the indexes. You should drop the indexes before squealing again.
The target row is inserted, or updated if present. We are using MySQL
INSERT ... UPDATE ON DUPLICATE KEY extended syntax to achieve this for now. This allows an event-driven update of exported data (e.g. through redis queues) as well as a bulk batch process.