HowTo:  Use Python to determine the SQL syntax for a WHERE clause depending on the workspace type

【解决方案】
The describe property, workspaceFactoryProgID, allows for the workspace type to be determined. An IF statement can then be used to write the correct WHERE clause based on this workspace type.

This is better than using workspaceType since it allows for more distinction between a file and personal geodatabase.


'WhereClause' is being used as a Python variable and not as an actual SQL WHERE clause.



The first sample looks at the layers in a map document with a hard-coded field value:
import arcpy

#makes map document object
mxd = arcpy.mapping.MapDocument(r"C:\Data\Maps\Sample.mxd")

#Predetermined FID that is needed.
value = "5"

layername = "states"

layers = arcpy.mapping.ListLayers(mxd, layername)

for layer in layers:
#finds the workspace path for the layer/Feature Class
WP = layer.workspacePath
print WP

#Creates a describe object for the workspace path
desWP = arcpy.Describe(WP)

#Pulls the workspace product type
WPtype = desWP.workspaceFactoryProgID
print WPtype

#Identifies File Geodatabase
if WPtype == "esriDataSourcesGDB.FileGDBWorkspaceFactory.1":
#sample where clause for fgdb data
WhereClause = '"ObjectID" = ' + value
print WhereClause

#Identifies Personal Geodatabase
if WPtype == "esriDataSourcesGDB.AccessWorkspaceFactory.1":
#sample where clause for mdb data
WhereClause = "[ObjectID] = " + value
print WhereClause

#Identifies SDE database
if WPtype == "esriDataSourcesGDB.SdeWorkspaceFactory.1":
#sample where clause for SDE data
WhereClause = "ObjectID = " + value
print WhereClause

#Other (Shapefile, coverage, CAD, VPF, and so on)
if WPtype == "":
#sample where clause for shapefile data
WhereClause = '"ObjectID"= ' + value
print WhereClause

del WhereClause

The second sample allows for a variable to pass the field name into the WHERE clause.
import arcpy

#makes map document object
mxd = arcpy.mapping.MapDocument(r"C:\Data\Maps\Sample.mxd")

#field name variable that is needed.
fieldname = "STATE"

#Predetermined value
value = "'NC'"

layername = "states"

layers = arcpy.mapping.ListLayers(mxd, layername)

for layer in layers:
#finds the workspace path for the layer/Feature Class
WP = layer.workspacePath
print WP

#Creates a describe object for the workspace path
desWP = arcpy.Describe(WP)

#Pulls the workspace product type
WPtype = desWP.workspaceFactoryProgID
print WPtype

#Identifies File Geodatabase
if WPtype == "esriDataSourcesGDB.FileGDBWorkspaceFactory.1":
#sample where clause for fgdb data
WhereClause = '"' + fieldname + '"= ' + value
print WhereClause

#Identifies Personal Geodatabase
if WPtype == "esriDataSourcesGDB.AccessWorkspaceFactory.1":
#sample where clause for mdb data
WhereClause = "[" + fieldname + "] = " + value
print WhereClause

#Identifies SDE database
if WPtype == "esriDataSourcesGDB.SdeWorkspaceFactory.1":
#sample where clause for SDE data
WhereClause = fieldname + "= " + value
print WhereClause

#Other (Shapefile, coverage, CAD, VPF, and so on)
if WPtype == "":
#sample where clause for shapefile data
WhereClause = '"' + fieldname + '"= ' + value
print WhereClause

del WhereClause



【其它相关参考】

1. ArcGIS 10 - Arcpy Site Package - Workspace properties
2. ArcGIS 10 - Building a query expression
3. ArcGIS 10 - SQL reference for query expressions used in ArcGIS
4. ArcGIS 10 - Select Layer By Attribute (Data Management)
5. ArcGIS 10 - Accessing data using cursors

【创建及修改时间】
Created: 6/7/2012

Last Modified: 7/10/2013
【原文链接】
http://support.esri.com/en/kno ... 40355