* sqlite3 from [sqlite](http://www.sqlite.org)

Community uses the following internal packages:

* tao from [tao](../tao/tao.md)
* tao-sqlite [tao-sqlite](../tao-sqlite/tao-sqlite.md)


## Options

* dbfile - Path to a file which stores the sqlite database for the community (default in-memory)
* virtual - Root Url of this object.

## Attached Objects

Community objects (and their derived classes) contain an embedded sqlite
database. This database can be accessed via that \<db\> method.

## Methods

Back to [tao](../tao.md)

tao-sqlite is a module of related classes which act as ambassadors to **sqlte** database connections.

# Sub-Modules

[yggdrasil](yggdrasil.md)

# Core Classes

## class taodb::connection

Implements a generic wrapper around a database connection. (Note: at this
point only sqlite has been developed.)

Ancestors: [tao.onion](../tao/onions.md)

### Methods

#### method active_layers

Return a list of database layers to act as ambassodors for various
collections of tables. See [onions](../tao/onions.md)

#### method Database_Create

Commands to invoke when the interface attempts to connect to a virgin
database. This method should build the database schema and populate any
starter data.

#### method Database_Functions

Inject functions into the database interface. For sqlite, this method
invokes the interface's native *function* method to map an sqlite function
to a Tcl command.

#### Ensemble schema

Ensemble to manage database schemas.

##### method schema create_sql

Return fully formed SQL code to implement the schema

The default implementation
is to interrogate the object layers for a *schema create_sql* property.

##### method schema tables

Return a list of tables specified by the schema. The default implementation
is to interrogate the object layers for a *schema table* property.

Onions have layers. Like ogres. Or parfaits.

# Class tao::layer

## Options

* prefix - A letter code for this layer
* layer\_name - A plaintext name for this layer.
* layer\_index\_order - Integer which expresses what order this layer should be index. (0 first -> infinity)

## Methods

### method node\_is\_managed *unit*

Returns true if an object or record described by *unit* is managed by this object.

### method type\_is\_managed *unit*

Returns true if an type, class or family of records described by *unit* is managed by this object.

# Class tao::onion

## Variables

* layers - A dict containing a mapping of layer names and the objects which implement them.

## Properties

* shared_organs - A list of stubs which are also connected to any node or layer spawned by this object.

## Methods

### method action activate_layers

Action to perform after all of the layer objects have been connected.

### method activate_layers ?1|0?

Using the output of *active_layers*, build a nest of layers. If a *1* is
given as the first argument, all existing layers are unmapped and destroyed
before mapping new layers. Otherwise layers that were previously mapped
and not present in the current incarnation of the object are destroyed. Layers
which exist in the current incarnation, but which arent't mapped are created.
Layers that are mapped, and present in the *active_layers*, but which
have a different class implementation morph into the new class.

### method active_layers

Return a dict describing the layers that should be mapped to this object.

Example:

    method active_layers {} {
      set result {
        xtype     {prefix y class sde.layer.xtype}
        eqpt      {prefix e class sde.layer.eqpt}
        portal    {prefix p class sde.layer.portal}
      }
      return $result
    }
    
### method layer *layerid* ?*method*? ?*args...*?

With only the *layerid* argument, return the object which implements
the layer described by *layerid*. If the layer does not exist, ::noop (a command which takes any argument
and does nothing) is returned.

If more arguments are specified, the command will exercise the *method* of the
layer object using any additional *args*.

Example:

    set obj [::db layer users]
    set username [$obj record_exists $userid]
    
    OR
    
    set exists [::db layer users record_exists $userid]

### method layers

Return a dict describing the layers currently mapped to this object.

### method Shared_Organs

Return a list of organs for this object which should also be grafted to
any layers or other nodes spawned by it. The default implementation is to
return the contents of the value of *property shared_organs*

### Method SubObject layer *name*

Return the fully qualified name of the object which will implement this layer.

The default implementation return \[namespace current\]::SubObject\_Layer\_\$name