Working with schemas: FeatureType
================================

The descriptors have information about name, type, accuracy,etc from the fields of our data containers.

Depending on its use they must meet some requirements. e.g. if we create a vectorial layer, its scheme have to have a field **GEOMETRY**


Create Schema
-------------

.. py:function:: createFeatureType([schema=None]):
    
    Create an empty schema. If parameter schema is a :javadoc:`DefaultEditableFeatureType <DefaultEditableFeatureType>`, creates a copy of this schema :javadoc:`DefaultFeatureType <DefaultFeatureType>`.
	
    :param schema: Schema from other layer
    :type schema: :javadoc:`DefaultEditableFeatureType <DefaultEditableFeatureType>`
    :return: empty schema or a copy of a schema
    :type return: DefaultEditableFeatureType

The interface :javadoc:`DataTypes <DataTypes>` specify a group of constant who indicate the kind of supported data for DAL.

We take a look how to create a schema with two fields and assignate them to a new table::


	from gvsig import *
	from gvsig.geom import *

	def main(*args):

		schema = createFeatureType() # DefaultFeatureType

		schema.append("ID", "INTEGER", 10) 
		schema.append("NAME", "STRING", 20)

		dbf = createDBF(schema)
		
		d = loadDBF( dbf.getFullName()) # Load a table on the project

Also we can create a new schema from already existing one, very useful when we want to make copies of layers. To move an schema for creating layers must be type **DefaultFeatureType**, the function :py:func:``createFeatureType()`` turn the schema type :javadoc:`DefaultEditableFeatureType <DefaultEditableFeatureType>` into the necesary::	


	from gvsig import *
	from gvsig.geom import *

	def main(*args):

		schema = createFeatureType() # DefaultFeatureType

		schema.append("ID", "INTEGER", 10)
		schema.append("NAME", "STRING", 20)

		dbf_1 = createDBF(schema)
		
		dbf_schema = dbf_1.getSchema() # DefaultEditableFeatureType

		# New schema based on another layer
		new_schema = createSchema(dbf_schema)
		new_schema.append("CODE", "STRING", 5)
		
		dbf_2 = createDBF(new_schema)

A manner to acces to the descriptors in the schema is through ``schema.get("Campo")``. Also we can iterate over them. In the following example, we see the way to add different fields from diferent types to a new schema. We have made a function who iterate over them to show the complete information about the schema we use like parameter, then::


	from gvsig import *
	from gvsig.geom import *

	def showInfoFeatureType(schema):
		#Show schema
		attrSchema = schema.getAttrNames()
		print "Schema attr: ", attrSchema
		#First field in schema
		field1 = schema.get(0)

		# Description of the fields
		print "\nFields description"
		for field in schema:
			print " Name: ", field.getName(),
			print " \tDataTypeName: ", field.getDataTypeName(),
			print " \tType: ", field.getType(),
			print " \tSubType: ", field.getSubtype(),
			print " \tPrecision: ", field.getPrecision(),
			print " \tSize: ", field.getSize()
			
			if field.getDataTypeName() == 'Geometry':
			  geomType = field.getGeomType()
			  print " \tGeom Name: ", geomType.getName()
			  print " \tGeom FullName: ", geomType.getFullName()
			  print " \tType: ", geomType.getType()
			  print " \tSubType: ", geomType.getSubType()
			  print " \tGeometryClass: ", geomType.getGeometryClass()
			  print " \tDimension: ", geomType.getDimension()

	def main(*args):

		schema = createFeatureType()

		schema.append("ID", "INTEGER", 10)
		schema.append("NAME", "STRING", 20)
		schema.append("AREA", "DOUBLE", 20, 10)
		schema.append("FECHA", "DATE", 20)
		schema.append("ACTIVE", "BOOLEAN")
		schema.append("GEOMETRY", "GEOMETRY")
		schema.get('GEOMETRY').setGeometryType(POINT, D2)

		shape = createShape(schema, prefixname="date")
		currentView().addLayer(shape)
		showInfoFeatureType(schema)
		
Console display::

	Schema attr:  [u'ID', u'NAME', u'AREA', u'FECHA', u'ACTIVE', u'GEOMETRY']

	Fields description
	 Name:  ID  	DataTypeName:  Integer  	Type:  4  	SubType:  None  	Precision:  0  	Size:  10
	 Name:  NAME  	DataTypeName:  String  	Type:  8  	SubType:  None  	Precision:  0  	Size:  20
	 Name:  AREA  	DataTypeName:  Double  	Type:  7  	SubType:  None  	Precision:  4  	Size:  20
	 Name:  FECHA  	DataTypeName:  Date  	Type:  9  	SubType:  Date  	Precision:  0  	Size:  20
	 Name:  ACTIVE  	DataTypeName:  Boolean  	Type:  1  	SubType:  None  	Precision:  0  	Size:  0
	 Name:  GEOMETRY  	DataTypeName:  Geometry  	Type:  66  	SubType:  Geometry  	Precision:  0  	Size:  0
		Geom Name:  Point2D
		Geom FullName:  Point:2D
		Type:  1
		SubType:  0
		GeometryClass:  <type 'org.gvsig.fmap.geom.jts.primitive.point.Point2D'>
		Dimension:  2

Modify Schema
-------------

In the following example, we're going to modify a schema::

	from gvsig import *
	from gvsig.geom import *

	def main(*args):

		schema = createFeatureType() # DefaultFeatureType

		schema.append("ID", "INTEGER", 10)
		schema.append("NAME", "STRING", 20)
		schema.append("CODE", "STRING", 2)
		
		
		# By index
		schema.remove(0)
		print "Remove descriptor ID: ", schema.getAttrNames()

		# By descriptor
		rm = schema.getEditableAttributeDescriptor("CODE")
		schema.remove(rm)
		print "Remove descriptor CODE: ", schema.getAttrNames()

		# Add geometry field
		schema.append("GEOMETRY", "GEOMETRY")
		schema.get("GEOMETRY").setGeometryType(POINT, D2)
		print "Add geometry field: ", schema.getAttrNames()
		
Console display::

	Remove descriptor ID:  [u'NAME', u'CODE']
	Remove descriptor CODE:  [u'NAME']
	Add geometry field:  [u'NAME', u'GEOMETRY']
		
		
Schema for vectorial layers
---------------------------

The creation of a vectorial layer it will be a very similar example, only should contain a field ``GEOMETRY` of type ``GEOMETRY``. After to create this field, we have to stablish the type of geometry will contain.

The following example shows the typical case of creation a new vectorial layer::

	from gvsig import *
	from gvsig.geom import *

	def main(*args):

		schema = createFeatureType() # DefaultFeatureType

		schema.append("ID", "INTEGER", 10)
		schema.append("NAME", "STRING", 20)
		schema.append("GEOMETRY", "GEOMETRY")
		schema.get("GEOMETRY").setGeometryType(POINT, D2)

		shape = createShape(schema)
		currentView().addLayer(shape)