Memento v0.3.2

View Source Memento.Schema (Memento v0.3.2)

Module to interact with the database schema.

For persisting data, Mnesia databases need to be created on disk. This module provides an interface to create the database on the disk of the specified nodes. Most of the time that is usually the node that the application is running on.

# Create schema on current node
Memento.Schema.create([ node() ]

# Create schema on many nodes
node_list = [node(), :alice@host_x, :bob@host_y, :eve@host_z]
Memento.Schema.create(node_list)

Important thing to note here is that only the nodes where data has to be persisted to disk have to be included. RAM-only nodes should be left out. Disk schemas can also be deleted by calling delete/1 and you can get information about them by calling info/0.

example

 Example 

# The nodes where you want to persist
nodes = [ node() ]

# Create the schema
Memento.stop
Memento.Schema.create(nodes)
Memento.start

# Create disc copies of your tables
Memento.Table.create!(TableA, disc_copies: nodes)
Memento.Table.create!(TableB, disc_copies: nodes)

Link to this section Summary

Functions

create(nodes)

Creates a new database on disk on the specified nodes.

delete(nodes)

Deletes the database previously created by create/1 on the specified nodes.

info()

Prints schema information about all Tables to the console.

info(table)

Prints schema information about the specified Table to the console.

set_storage_type(node, type)

Sets the schema storage mode for the specified node.

Link to this section Functions

Link to this function

create(nodes)

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Specs

create([node()]) :: :ok | {:error, any()}

Creates a new database on disk on the specified nodes.

Calling :mnesia.create_schema for a custom path throws an exception if that path does not exist. Memento's version avoids this by ensuring that the directory exists.

Also see :mnesia.create_schema/1.

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delete(nodes)

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Specs

delete([node()]) :: :ok | {:error, any()}

Deletes the database previously created by create/1 on the specified nodes.

Use this with caution, as it makes persisting data obsolete. Also see :mnesia.delete_schema/1.

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info()

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Specs

info() :: :ok

Prints schema information about all Tables to the console.

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info(table)

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Specs

info(Memento.Table.name()) :: :ok

Prints schema information about the specified Table to the console.

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set_storage_type(node, type)

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Specs

set_storage_type(node(), Memento.Table.storage_type()) :: :ok | {:error, any()}

Sets the schema storage mode for the specified node.

Useful when you want to change the schema mode on the fly, usually when connecting to a new, unsynchronized node on discovery at runtime.

The mode can only be :ram_copies or :disc_copies. If the storage mode is set to ram_copies, then no table on that node can be disc-resident.

This just calls Memento.Table.set_storage_type/3 underneath with :schema as the table. Also see :mnesia.change_table_copy_type/3 for more details.

example

 Example 

Memento.Schema.set_storage_type(:node@host, :disc_copies)