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Amazon DynamoDB

Create

10 samples, from the least code that works to complete workflows.

What a create does

Rule On DynamoDB
Where it goes The model says: a table of the entity's own (.Table("product", partitionKey: "sku")), or a single table shared by several entities, whose keys are templates (PK = CUSTOMER#{customer_id})
The keys ARX writes the table's key attributes, the index keys and entity_type from the model; the entity gives the values the templates name
An index's attributes A create may leave out an attribute an index key is made of (a GSI is sparse): the item is written without that index key and isn't in the index, so a query through the index doesn't find it. An update that writes some of an index key's attributes must give the rest (ARX1001), because ARX writes the whole index key again; give none to leave the index key as it is
The id Supplied by the application: DynamoDB generates no ids, so a generated id is ARX8001 (give a Guid.CreateVersion7() or your own)
A duplicate ARX3001 UniqueViolation: every create is a conditional put (attribute_not_exists) and never overwrites
Names ASCII letters, digits and _; #, : (expression syntax) or SQL syntax is ARX1017; names reach DynamoDB only as placeholders
Key values Escaped in templates (# is stored as %23, % as %25), so a value can't make another entity's key
Write sharding .WriteSharding(entity, shards, by) adds #SHARD#n to the partition key, n from a stable hash of the by attribute
Size An item over 400 KB is ARX4002
Without a catalog Nothing to resolve: the ArxDynamoModel declares every table's keys and ids, and DynamoDB declares no column types. The SQL providers' SchemaResolution doesn't apply

Reference

Value types

.NET value Stored as
string S (string); an empty key value is ARX1001
char S
a plain enum refused (ARX1007): write (int)value or value.ToString(), or use a selection set
int, long, short, byte and the unsigned types N (number)
decimal N, exact up to 38 digits (more is ARX4001)
double, float N; NaN and infinity are ARX4001
bool BOOL
Guid S, D format (5f0c…-…)
byte[], ArxBytea B (binary)
ArxJsonB M (map) or L (list), its JSON parsed
an array or a list L, a list of the values above
ArxSelectionSetValue its code, checked against the catalog
ArxEntityReference the referenced id, checked against the catalog (ARX1005)
null NULL

Dates and times

DynamoDB has no date type: ARX stores dates as sortable text, so a sort key or a condition on a date compares in time order.

.NET value Stored as
DateTime (UTC) S, 2026-11-09T10:30:00.0000000Z (every tick kept)
DateTime (Local) converted to UTC
DateTime (Unspecified) taken as UTC
DateTimeOffset its UTC instant (the offset isn't kept)
DateOnly S, 2026-11-09
TimeOnly, TimeSpan S (09:30:00.0000000, 1.02:03:04)
default(DateTime), default(DateTimeOffset), default(DateOnly) refused (ARX1013): they mean "not set"

The samples

Basics

The least code that works.

1Create one record, in either designProgressive

The smallest create, in the two designs DynamoDB tables are made in: an entity with a table of its own, then a customer and an order sharing one table through key templates.

2Catch the errors a create meetsProgressive

The errors a create meets most, in three scenarios: a key that exists, a key attribute left out, and an id declared as generated, which DynamoDB can't do.

Real cases

What an application does: a small CRM and product catalogue.

1Store every kind of valueProgressive

What each .NET value becomes in DynamoDB, in two scenarios: numbers, text and flags; then dates, documents, lists and picklists.

2Catch an injection attemptProgressive

A form whose fields become attributes, attacked three ways: an expression placeholder as a field name, SQL in a field name, and key separators in a value meant to land on another customer's key.

Advanced cases

Dependency injection, transactions, batch scopes and setting the service up.

1Create in an ARX transactionAdvanced

Writes across tables in one ARX transaction, in two scenarios: committed together, and a commit that fails and writes nothing.

2A security check around createsAdvanced

A security check around creates (SecurityGuard, in the project root), in three scenarios: a normal request, an attack that is logged, and repeated attacks that block the user.

3Set up the service from DynamoDB's tablesAdvanced

The service set up from DynamoDB's own description of its tables, in two scenarios: preload the lead table's key at startup, then create with Strict on, where only the declared attributes may be written.

4Set the service up for productionAdvanced

Set the service up for production, in three scenarios: depend on IArxDataService, check the server at startup, and trace and measure every call.

5Use attributes named outside the name rule, through aliasesAdvanced

Use items whose attributes are named outside ARX's name rule, in three scenarios: declare an alias for each such attribute and create items through them, read and query by the aliases, and see what is still refused: the attribute's own name in a call, and an alias on an attribute the model names.

6Log every call through ILoggerAdvanced

Log every ARX call through ILogger, in three scenarios: one line per call with its table and how long it took, a failed call with its ARX code (and the exception logged where it is caught), and only the calls worth keeping in production.