Zusammenfassung
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.
Diskussion
Das FieldMappings-Objekt ist eine Sammlung von FieldMap-Objekten und wird als Parameterwert für Werkzeuge für die Feldzuordnung verwendet, beispielsweise Zusammenführen (Merge). Sie können am einfachsten mit diesen Objekten arbeiten, indem Sie zuerst ein FieldMappings-Objekt erstellen und dann die zugehörigen FieldMap-Objekte initialisieren, indem Sie die zu kombinierenden Eingabe-Feature-Classes oder Tabellen hinzufügen. Wenn alle Eingaben bereitgestellt wurden, enthält das FieldMappings-Objekt ein FieldMap-Objekt (bzw. ein Ausgabefeld) für jeden eindeutigen Feldnamen aus allen Eingaben. Sie können diese Liste ändern, indem Sie neue Felder hinzufügen, die Eigenschaften und/oder den Inhalt von Ausgabefeldern ändern oder unerwünschte Ausgabefelder entfernen.
Die Eigenschaften des FieldMap-Objekts enthalten die Anfangs- und die Endposition eines Eingabetextwertes, sodass ein neuer Ausgabewert mit einem Teil eines Eingabewertes erstellt werden kann. Wenn ein FieldMap-Objekt mehrere Eingabefelder aus derselben Tabelle oder Feature-Class enthält, werden die Werte aller Datensätze unter Verwendung der Eigenschaft MergeRule zusammengeführt. Dies ist eine benutzerfreundliche Möglichkeit zum Verbinden von Werten, beispielsweise eines Straßennamens in einem Feld und einer Straßenart, die in einem anderen Feld enthalten ist (z. B. "Eureka" und "Street"). Der joinDelimiter-Eigenschaft eines FieldMap-Objekts wird verwendet, wenn der mergeRule-Wert Join angegeben wird. Als Trennzeichen können beliebige Zeichen verwendet werden, beispielsweise Leerzeichen. Im obigen Beispiel würde damit der Wert "Eureka Street" erstellt.
Syntax
FieldMappings ()
Eigenschaften
| Eigenschaft | Erläuterung | Datentyp |
| fieldCount (Schreibgeschützt) | The number of output fields. | Integer |
| fieldMappings (Lesen und schreiben) | A list of FieldMap objects that make up the FieldMappings object. | FieldMap |
| fieldValidationWorkspace (Lesen und schreiben) | 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 (Schreibgeschützt) | A list of Field objects. Each field object represents the properties of each output field. | Field |
Methodenübersicht
| Methode | Erläuterung |
| 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. |
Methoden
addFieldMap (field_map)
| Parameter | Erläuterung | Datentyp |
field_map | The field map to add to the field mappings | FieldMap |
addTable (table_dataset)
| Parameter | Erläuterung | Datentyp |
table_dataset | The table to add to the field mappings object. | String |
exportToString ()
Rückgabewert
| Datentyp | Erläuterung |
| String | The string representation of the object. |
findFieldMapIndex (field_map_name)
| Parameter | Erläuterung | Datentyp |
field_map_name | Find the field map by name. | String |
Rückgabewert
| Datentyp | Erläuterung |
| Integer | The index position of the field map. |
getFieldMap (index)
| Parameter | Erläuterung | Datentyp |
index | The index position of the field map. | Integer |
Rückgabewert
| Datentyp | Erläuterung |
| FieldMap | The field map from the field mappings. |
loadFromString (string)
| Parameter | Erläuterung | Datentyp |
string | The string representation of the object. | String |
removeAll ()
removeFieldMap (index)
| Parameter | Erläuterung | Datentyp |
index | The index position of the field map. | Integer |
replaceFieldMap (index, value)
| Parameter | Erläuterung | Datentyp |
index | The index position of the field map to be replaced. | Integer |
value | The replacement field map. | FieldMap |
Codebeispiel
FieldMappings example
FieldMap objects are often used when there is a need to merge similar datasets into one, all-encompassing dataset. In this example, the feature class Trees and the shapefile Plants.shp are merged into one feature class: Vegetation. Both original feature classes have two attributes: Type and Diameter. These two attributes must be maintained through the merge.
import arcpy
# Set the workspace
arcpy.env.workspace = 'c:/base'
in_file1 = 'data.gdb/Trees'
in_file2 = 'Plants.shp'
output_file = 'data.gdb/Vegetation'
# Create the required FieldMap and FieldMappings objects
fm_type = arcpy.FieldMap()
fm_diam = arcpy.FieldMap()
fms = arcpy.FieldMappings()
# Get the field names of vegetation type and diameter for both original
# files
tree_type = "Tree_Type"
plant_type = "Plant_Type"
tree_diam = "Tree_Diameter"
plant_diam = "Diameter"
# Add fields to their corresponding FieldMap objects
fm_type.addInputField(in_file1, tree_type)
fm_type.addInputField(in_file2, plant_type)
fm_diam.addInputField(in_file1, tree_diam)
fm_diam.addInputField(in_file2, plant_diam)
# Set the output field properties for both FieldMap objects
type_name = fm_type.outputField
type_name.name = 'Veg_Type'
fm_type.outputField = type_name
diam_name = fm_diam.outputField
diam_name.name = 'Veg_Diam'
fm_diam.outputField = diam_name
# Add the FieldMap objects to the FieldMappings object
fms.addFieldMap(fm_type)
fms.addFieldMap(fm_diam)
# Merge the two feature classes
arcpy.Merge_management([in_file1, in_file2], output_file, fms)
FieldMappings example 2
This sample displays the option of using FieldMap objects to merge fields, using the FeatureClassToFeatureClass tool. In this example, a feature class contains information about the number of accidents per intersection in a city. Each year of data is maintained in one field. The user would like to find the average number of accidents in each intersection, without altering the existing table.
import arcpy
# Set the workspace
arcpy.env.workspace = 'c:/base/data.gdb'
in_file = 'AccidentData'
out_file = 'AverageAccidents'
# Create the necessary FieldMap and FieldMappings objects
fm = arcpy.FieldMap()
fm1 = arcpy.FieldMap()
fms = arcpy.FieldMappings()
# Each field with accident data begins with 'Yr' (from Yr2007 to Yr2012).
# The next step loops through each of the fields beginning with 'Yr',
# and adds them to the FieldMap Object
for field in arcpy.ListFields(in_file, 'Yr*'):
fm.addInputField(in_file, field.name)
# Set the merge rule to find the mean value of all fields in the
# FieldMap object
fm.mergeRule = 'Mean'
# Set properties of the output name.
f_name = fm.outputField
f_name.name = 'AvgAccidents'
f_name.aliasName = 'AvgAccidents'
fm.outputField = f_name
# Add the intersection field to the second FieldMap object
fm1.addInputField(in_file, "Intersection")
# Add both FieldMaps to the FieldMappings Object
fms.addFieldMap(fm)
fms.addFieldMap(fm1)
# Create the output feature class, using the FieldMappings object
arcpy.FeatureClassToFeatureClass_conversion(
in_file, arcpy.env.workspace, out_file, field_mapping=fms)