Expressions - Python

Jump to the Code block for a combined complete example.

This page describes how to use expressions in single record commands.

Aerospike expressions are a strongly typed, functional, domain-specific language for manipulating and comparing bins and record metadata.

For expression usage within multi-record requests, see Batch operations and Queries.

Setup

The examples on this page use the following setup and record structure to illustrate the use of expressions in single record commands.

import aerospike
from aerospike_helpers import expressions as exp
from aerospike_helpers.operations import expression_operations, map_operations, operations

# Define host configuration
config = {
    'hosts': [ ('127.0.0.1', 3000) ]
}
# Establishes a connection to the server
client = aerospike.client(config).connect()

# Creates a key with the namespace "sandbox", set "ufodata", and user key 5001
key = ('sandbox', 'ufodata', 5001)

The record structure:

+------+----------+----------+----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------+
| PK   | occurred | reported | posted   | report                                                                                                                                                                                                                 | location                                                   |
+------+----------+----------+----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------+
| 5001 | 20220531 | 20220601 | 20220601 | MAP('{"shape":["circle", "flash", "disc"], "summary":"Large flying disc flashed in the sky above the student union. Craziest thing I've ever seen!", "city":"Ann Arbor", "state":"Michigan", "duration":"5 minutes"}') | GeoJSON('{"type":"Point","coordinates":[42.2808,83.743]}') |
+------+----------+----------+----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------+

Filter expressions

Record filtering expressions select records that satisfy a boolean expression and work with all single record commands (reads, writes, operations, and record UDFs), batch reads, and queries. Filters are only executed when a record exists. Filters are not executed when a record is created or is not found.

Read

When using a Filter Expression on a read command, the expression is defined within the read policy.

The following example creates a filter expression that checks the length of the shape list in the report map and only returns if there are more than two shapes.

# Build the expression
expr = exp.GT(
    exp.ListSize(
        None,
        exp.MapGetByKey(None, aerospike.MAP_RETURN_VALUE, exp.ResultType.LIST, 'shape', exp.MapBin('report'))
    ),
    2).compile()

# Create the policy
policy = {'expressions': expr}

# Read the record
(key_, meta, bins) = client.get(key, policy=policy)

# Do something
print('Record: ', bins)

# Close the connection to the server
client.close()

Write

When using a Filter Expression on a write command, the expression is defined within the write policy.

The following example creates a filter expression that checks if occurred is later than 20211231 and posted exists. If the filter returns true, a recent key with the value true will be added to the report map.

# Build the expression
expr = exp.And(
        exp.GT(exp.IntBin('occurred'), 20211231),
        exp.BinExists('posted')).compile()

# Create the policy
policy = {'expressions': expr}

# Create map policy
map_policy = {'map_write_flags': aerospike.MAP_WRITE_FLAGS_DEFAULT}

# Create operations
ops = [map_operations.map_put('report', 'recent', True, map_policy)]

# Update the record
(key_, meta, bins) = client.operate(key, ops, policy=policy)

# Close the connection to the server
client.close()

Operation expressions

Operation expressions are bin operations that atomically compute a value from information within the record or provided by the expression. The result is either returned to the client, in a read expression, or written to a specified bin, in a write expression.

You can define a record filter expression in the write policy of the operate method to determine the execution of a bin operation using an operation expression.

Read

The read expression operation computes an expression, and returns that value. A defined name in the operation can be used as the synthetic bin name when retrieving results.

The following example takes the Read Filter Expression example from above and changes the scenario slightly. This command computes the length of the shape list in the report map and returns the value in a synthetic bin called numShapes.

# Build the expression
expr = exp.ListSize(
    None,
    exp.MapGetByKey(None, aerospike.MAP_RETURN_VALUE, exp.ResultType.LIST, 'shape', exp.MapBin('report'))).compile()

# Create operations
ops = [expression_operations.expression_read('numShapes', expr, aerospike.EXP_READ_DEFAULT)]

# Read the record
(keys_, meta, bins) = client.operate(key, ops)

# Do something
print('Record: ', bins)

# Close the connection to the server
client.close()

Write

The write expression operation computes an expression and writes that value to a bin.

The following example takes the Write Filter Expression example from above and changes the scenario slightly. Using the same criteria to compute a recent value, reported bin value and posted bin exists, this command updates the report map with the recent value, true or false.

# Build the expression
expr = exp.MapPut(None, None, 'recent',
    exp.And(
        exp.GT(exp.IntBin('occurred'), 20211231),
        exp.BinExists('posted')
    ),
    exp.MapBin('report')).compile()

# Create operations
ops = [expression_operations.expression_write('report', expr, aerospike.EXP_WRITE_DEFAULT)]

# Update the record
client.operate(key, ops)

# Close the connection to the server
client.close()

Code block

Expand this section for a single code block to create a Operation Expression

import aerospike
from aerospike_helpers import expressions as exp
from aerospike_helpers.operations import expression_operations, map_operations, operations

# Define host configuration
config = {
    'hosts': [ ('127.0.0.1', 3000) ]
}
# Establishes a connection to the server
client = aerospike.client(config).connect()

# Creates a key with the namespace "sandbox", set "ufodata", and user key 5001
key = ('sandbox', 'ufodata', 5001)

# Build the expression
expr = exp.MapPut(None, None, 'recent',
    exp.And(
        exp.GT(exp.IntBin('occurred'), 20211231),
        exp.BinExists('posted')
    ),
    exp.MapBin('report')).compile()

# Create operations
ops = [expression_operations.expression_write('report', expr, aerospike.EXP_WRITE_DEFAULT)]

# Update the record
client.operate(key, ops)

# Close the connection to the server
client.close()

History of expressions in Aerospike Database

Secondary index expressions introduced in Database 8.1.0
Operation expressions introduced in Database 5.6.0
XDR filter expressions introduced in Database 5.3.0
Record filter expressions introduced in Database 5.2.0