When adding a new record to a table, you must use the insert cursor. Here's the workflow for insert cursors:
- Create the insert cursor using arcpy.da.InsertCursor().
- Call InsertCursor.insertRow() to add a new row to the dataset.
As with the search and update cursor, you can use an insert cursor together with the "with" statement to avoid locking problems.
Insert cursors differ from search and update cursors in that you cannot provide an SQL expression when you create the insert cursor. This makes sense because an insert cursor is only concerned with adding records to the table. It does not need to "know" about the existing records or any subset thereof.
When you insert a row using InsertCursor.insertRow(), you provide a comma-delimited tuple of values for the fields of the new row. The order of these values must match the order of values of the tuple of affected fields you provided when you created the cursor. For example, if you create the cursor using
with arcpy.da.InsertCursor(featureClass, ("FirstName","LastName")) as cursor:
you would add a new row with values "Sam" for "FirstName" and "Fisher" for "LastName" by the following command:
Please note that the inner parentheses are needed to turn the values into a tuple that is passed to insertRow(). Writing cursor.insertRow("Sam","Fisher") would have resulted in an error.
The example below uses an insert cursor to create one new point in the dataset and assign it one attribute: a string description. This script could potentially be used behind a public-facing 311 application, in which members of the public can click a point on a Web map and type a description of an incident that needs to be resolved by the municipality, such as a broken streetlight.
# Adds a point and an accompanying description import arcpy # Retrieve input parameters inX = arcpy.GetParameterAsText(0) inY = arcpy.GetParameterAsText(1) inDescription = arcpy.GetParameterAsText(2) # These parameters are hard-coded. User can't change them. incidentsFC = "C:/Data/Yakima/Incidents.shp" descriptionField = "DESCR" # Make a tuple of fields to update fieldsToUpdate = ("SHAPE@XY", descriptionField) # Create the insert cursor with arcpy.da.InsertCursor(incidentsFC, fieldsToUpdate) as cursor: # Insert the row providing a tuple of affected attributes cursor.insertRow(((float(inX),float(inY)), inDescription)) del cursor
Take a moment to ensure that you know exactly how the following is done in the code:
- The creation of the insert cursor with a tuple of affected fields stored in variable fieldsToUpdate
- The insertion of the row through the insertRow() method using variables that contain the field values of the new row
If this script really were powering an interactive 311 application, the X and Y values could be derived from a point a user clicked on the Web map rather than as parameters as done in lines 4 and 5.
One thing you might have noticed is that the string "SHAPE@XY" is used to specify the Shape field. You might expect that this would just be "Shape," but arcpy.da provides a list of "tokens" that you can use if the field will be specified in a certain way. In our case, it would be very convenient just to provide the X and Y values of the points using a tuple of coordinates. It turns out that the token "SHAPE@XY" allows you to do just that. See the documentation of the InsertCursor's field_names parameter to learn about other tokens you can use.
Putting this all together, the example creates a tuple of affected fields: ("SHAPE@XY", "DESCR"). Notice that in line 13, we actually use the variable descriptionField which contains the name of the second column "DESCR" for the second element of the tuple. Using a variable to store the name of the column we are interested in allows us to easily adapt the script later, for instance to a data set where the column has a different name. When the row is inserted, the values for these items are provided in the same order: cursor.insertRow(((float(inX), float(inY)), inDescription)). The argument passed to insertRow() is a tuple that contains another tuple (inX,inY), namely the coordinates of the point cast to floating point numbers, as the first element and the text for the "DESCR" field as the second element.
Take a few minutes to read Zandbergen 8.1 - 8.3 to reinforce your learning about cursors.