FieldMappings

Resumen

The FieldMappings object is a collection of FieldMap objects and it is used as the parameter value for tools that perform field mapping such as Merge.

Debate

El objeto FieldMappings es una colección de objetos FieldMap y se utiliza como valor de parámetro para las herramientas que realizan la asignación de campos, tales como Merge. La manera más fácil de trabajar con estos objetos es crear primero un objeto FieldMappings y, a continuación, inicializar sus objetos FieldMap agregando las clases de entidad o las tablas de entrada que se vayan a combinar. Una vez proporcionadas todas las entradas, el objeto FieldMappings contendrá un objeto FieldMap, o campo de salida, para cada nombre de campo único de todas las entradas. Esta lista se puede modificar agregando nuevos campos, modificando las propiedades o los contenidos de un campo de salida, o quitando los campos de salida no deseados.

Las propiedades del objeto FieldMap incluyen la posición de inicio y final de un valor de texto de entrada, de modo que se pueda crear un nuevo valor de salida utilizando una sección de un valor de entrada. Si un objeto FieldMap contiene varios campos de entrada de la misma tabla o clase de entidad, los valores de cada registro se combinan utilizando la propiedad mergeRule. Ésta es una manera conveniente de unir valores, tales como un nombre de calle contenido en un campo y un tipo de calle contenido en otro, por ejemplo, Eureka y Street. La propiedad joinDelimiter de FieldMap si se utiliza si se especifica el valor de mergeRule Join. Cualquier conjunto de caracteres, tal como un espacio, se puede utilizar como delimitador. En el ejemplo anterior, esto crearía el valor Eureka Street.

Sintaxis

FieldMappings ()

Propiedades

Propiedad	Explicación	Tipo de datos
fieldCount (Sólo lectura)	The number of output fields.	Integer
fieldValidationWorkspace (Lectura y escritura)	The workspace type that defines the rules for attribute field naming. These rules are used when determining the output field names, which are based on the names of the input fields. For example, setting the fieldValidationWorkspace property to the path of a folder on disk containing the input shapefiles will result in the output field names being truncated to 10 characters. Setting the fieldValidationWorkspace property to the path of a file geodatabase will allow for much longer field names. The fieldValidationWorkspace property should be set with a consideration for the output format.	String
fields (Sólo lectura)	A Python List that contains a list of field objects. Each field object represents the properties of each output field.	Field

Vista general del método

Método	Explicación
addFieldMap (field_map)	Add a field map to the field mappings.
addTable (table_dataset)	Adds a table to the field mappings object.
exportToString ()	Exports the object to its string representation.
findFieldMapIndex (field_map_name)	Find a field map within the field mappings by name.
getFieldMap (index)	Gets a field map from the field mappings.
loadFromString (string)	Restore the object using its string representation. The exportToString method can be used to create a string representation.
removeAll ()	Removes all values and creates an empty object.
removeFieldMap (index)	Removes a field map from the field mappings.
replaceFieldMap (index, value)	Replace a field map within the field mappings.

Métodos

addFieldMap (field_map)

Parámetro	Explicación	Tipo de datos
field_map	The field map to add to the field mappings	FieldMap

addTable (table_dataset)

Parámetro	Explicación	Tipo de datos
table_dataset	The table to add to the field mappings object.	String

exportToString ()

Valor de retorno

Tipo de datos	Explicación
String	The string representation of the object.

findFieldMapIndex (field_map_name)

Parámetro	Explicación	Tipo de datos
field_map_name	Find the field map by name.	String

Valor de retorno

Tipo de datos	Explicación
Integer	The index position of the field map.

getFieldMap (index)

Parámetro	Explicación	Tipo de datos
index	The index position of the field map.	Integer

Valor de retorno

Tipo de datos	Explicación
FieldMap	The field map from the field mappings.

loadFromString (string)

Parámetro	Explicación	Tipo de datos
string	The string representation of the object.	String

removeAll ()

removeFieldMap (index)

Parámetro	Explicación	Tipo de datos
index	The index position of the field map.	Integer

replaceFieldMap (index, value)

Parámetro	Explicación	Tipo de datos
index	The index position of the field map to be replaced.	Integer
value	The replacement field map.	FieldMap

Ejemplo de código

FieldMappings example

import arcpy
from arcpy import env

# Input feature classes contain a PID field that is a composite of
#   the Township, Range, Section, QuarterSection, Block, Lot, and SubLot values.
#   We need to define how to break the PID field into two fields: TWNSHIP and BLOCK,
#   then run the Merge tool.
#   PID field and field map. 
#                    1 1 1 1 1 1 1
#  1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
# +-------------------------------+
# |2|0|3|0|8|2|1|0|0|1|0|0|5|0|0|0|
# +-------------------------------+
# +---TWNSHIP---+-------BLOCK-----+

infc1 = "C:/Data/NewParcels.shp"
infc2 = "Parcels"
outfc = "Parcels_Merge"

# Create a fieldmappings object and two fieldmap objects
#
fieldmappings = arcpy.FieldMappings()
fldmap_TWNSHIP = arcpy.FieldMap()
fldmap_BLOCK = arcpy.FieldMap()

# Create a value table to hold names of input feature classes for Merge tool.
#
vt = arcpy.ValueTable()

# Add all fields from first input feature class to fieldmappings object
#   AddTable is the most efficient way.
#
fieldmappings.addTable(infc1)

# Add the TWNSHIP and BLOCK field from the first input feature class 
#   to fieldmap object.
#
fldmap_TWNSHIP.addInputField(infc1)
fldmap_BLOCK.addInputField(infc1)
vt.addRow(infc1)

# Add all fields from second input feature class to fieldmappings object
#
env.workspace = "C:/Data/Boulder.gdb"
fieldmappings.addTable(infc2)

# Add the TWNSHIP and BLOCK field from the second input feature class 
#   to fieldmap object.
#
fldmap_TWNSHIP.addInputField(infc2)
fldmap_BLOCK.addInputField(infc2)
vt.addRow(infc2)

# Set the starting and ending positions of the input field in the fieldmap.
#   This is for TWNSHIP
for x in range(0, fldmap_TWNSHIP.inputFieldCount):
    fldmap_TWNSHIP.setStartTextPosition(x, 0)
    fldmap_TWNSHIP.setEndFieldPosition(x, 6)

# Set the starting and ending positions of the input field in the fieldmap.
#   This is for BLOCK
for x in range(0, fldmap_BLOCK.inputFieldCount):
    fldmap_BLOCK.setStartTextPosition(x, 7)
    fldmap_BLOCK.setEndFieldPosition(x, 15)

# Get the new field object from fieldmap, set field name, place back in fieldmap.
#
fld_TWNSHIP = fldmap_TWNSHIP.outputField
fld_TWNSHIP.name = "TWNSHIP"
fldmap_TWNSHIP.outputField = fld_TWNSHIP
fld_BLOCK = fldmap_BLOCK.outputField
fld_BLOCK.name = "BLOCK"
fldmap_BLOCK.outputField = fld_BLOCK

# Add the new fieldmap object to fieldmappings object.
fieldmappings.addFieldMap(fldmap_TWNSHIP)
fieldmappings.addFieldMap(fldmap_BLOCK)

#Run the Merge tool
arcpy.Merge_management(vt, outfc, fieldmappings)