bcquality/microsoft/knowledge/performance/use-dictionary-for-temporary-identity-lookups.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	dictionary temporary-table lookup identity o1	al	w1	all

Use Dictionary for temporary identity lookups

Description

A temporary record is useful when code needs record semantics: filters, keys, FlowFields, or table-shaped buffers. When the only operation is "have I seen this key?" or "what value belongs to this key?", a Dictionary is the simpler and faster structure. Dictionary lookup is O(1) by key, while a temporary table still pays record and key-management overhead.

Best Practice

Use Dictionary for in-memory lookup sets and maps whose keys fit in memory and whose access pattern is by identity. Keep temporary tables for data that needs table APIs, multiple keys, filter expressions, or later processing as records.

See sample: use-dictionary-for-temporary-identity-lookups.good.al.

Anti Pattern

Creating a temporary table solely to call Get or FindFirst by a single key in a loop. The code looks familiar to AL developers, but it is heavier than the lookup problem requires.

See sample: use-dictionary-for-temporary-identity-lookups.bad.al.