Expressions

Expressions are the small DSL DynamoDB uses for conditional writes, partial updates, key matching, and column projection. They're easy to fumble: reserved words, placeholder syntax, and the difference between a condition that's checked atomically and a filter that runs after the read.

This section pulls the four expression families apart so you know which one does what, then explains the placeholder mechanics they all share.

0 of 6 readQuiz

DynamoDB Condition Expressions

How DynamoDB condition expressions enforce invariants like "no overdraft" inside a single write, why they replace SELECT-then-UPDATE, and how to write them.

Intermediate5 min read

DynamoDB Update Expressions

How DynamoDB update expressions work — SET, ADD, REMOVE, DELETE — and which one to reach for, with a shopping-cart worked example.

Intermediate5 min read

DynamoDB Key Condition Expressions

How DynamoDB key condition expressions work — the operators allowed on the sort key, begins_with vs BETWEEN, and why a filter is not a substitute.

Intermediate5 min read

DynamoDB Projection Expressions

DynamoDB projection expressions return only the attributes you name — cut payload and item size. What they do (and don't) save on read cost, with a worked example.

Beginner6 min read

Expression Attribute Names and Values in DynamoDB

How DynamoDB expression attribute names (#name) and values (:value) work, why reserved words like status and size break your query, and how to fix it.

Intermediate5 min read

Knowledge checkTake the quiz

Check what you’ve learned in this section.

Start with condition expressions; the others build on the same syntax.

Try DynoTable to build and run these expressions without escaping JSON by hand.