Supported data types

.NET value	Column	Stored as
string	text, varchar(n), char(n)	as written (char(n) pads with spaces)
short / int / long	smallint / int / bigint	32000 / 2000000000 / 9000000000000
decimal	numeric(p, s)	12345.678901
float / double	real / double precision	3.25 / 2.718281828459045
bool	boolean	true
Guid	uuid	6f9619ff-8b86-d011-b42d-00c04fc964ff
DateTime (Kind Utc), DateTimeOffset	timestamptz	the UTC instant: 2026-11-07 14:30:00+00
DateTime (Kind Unspecified)	timestamp	as written: 2026-11-07 09:00:00
DateOnly / TimeOnly / TimeSpan	date / time / interval	2026-11-07 / 17:45:30 / 1 day 12:30:00
byte[], ArxBytea	bytea	\xcafe
ArxJsonB	jsonb	the JSON
string[], int[], decimal[], Guid[], DateOnly[], DateTime[], …	text[], int[], …	{red,green}, {1,2,3}, …
ArxEntityReference	the lookup column	the referenced id
ArxSelectionSetValue	the set's column	the option's code
null	any	NULL
byte, sbyte / ushort / uint / ulong	converted to smallint / int / bigint / numeric	200 / 65000 / 4000000000 / 18446744073709551615
char	text	X
a plain enum	refused (ARX1007)	write (int)value or value.ToString(), or use a selection set, which stores the code its set declares
DateTime with Kind Local	timestamptz	converted to UTC

Any other type is refused before anything is sent (ARX1007 UnsupportedValueType): write uri.ToString() rather than a Uri. RealCase2_EveryDataType writes every row of this table and prints what PostgreSQL stored.

With the column types preloaded (ArxPreLoadMode.DataTypes), a number with a fraction written to a whole-number column is refused before PostgreSQL (ARX4001 ValueOutOfRange) on a create, an update and a write by a filter, where PostgreSQL would round it (7.9 stored as 8); a condition in a read (qty < 7.5) isn't refused. A NaN or an infinity written to a declared decimal column is refused the same way. Without declared types, PostgreSQL stores a double NaN in a numeric column, and it reads back as a double.

You have	Use	Column
A moment (an order was placed)	DateTimeOffset, or DateTime with Kind Utc	timestamptz
A wall-clock time with no zone	DateTime with Kind Unspecified	timestamp
A calendar date	DateOnly	date
A time of day	TimeOnly	time
A duration	TimeSpan	interval

The same moment written as a DateTimeOffset (+08:00), a UTC DateTime or a local DateTime is stored as the same instant. A DateTime with Kind Unspecified written to a timestamptz column is read in the session's time zone: ARX's own connections are UTC (Timezone=UTC), so 09:00 is stored as 09:00+00; a connection string that names another zone (Timezone=Asia/Manila) makes it 01:00+00. Give a moment Kind Utc, or a DateTimeOffset, so the session can't change it. Refused: default(DateTime) (ARX1013: it means "not set", and PostgreSQL would store -infinity; use null), and a date given as a string (ARX4004: ARX never parses strings as dates). Full rules: Data types.

PostgreSQL column	Reads back as	Notes
text, varchar(n), char(n)	string	char(n) keeps its padding spaces; "" stays ""
smallint / integer / bigint	short / int / long
numeric(p, s)	decimal	More than 28 significant digits: ARX4001 ValueOutOfRange. NaN, Infinity and -Infinity, which a numeric can hold and a decimal can't, read back as a double (from 0.1.0-preview.5; the read failed before)
real / double precision	float / double
boolean	bool
uuid	Guid
timestamptz	DateTime, Kind Utc	The instant, in UTC whatever the session's time zone
timestamp	DateTime, Kind Unspecified	The wall-clock time as stored
date / time / interval	DateOnly / TimeOnly / TimeSpan	An interval with months or years: ARX4004 DataTypeMismatch (a TimeSpan can't hold one)
bytea	byte[]
json, jsonb	ArxJsonB	SerializedValue holds the JSON text
An array (text[], int[], date[], …)	T[] (string[], int[], DateOnly[], …)	With NULL elements, a value type reads as T?[] (int?[])
An enum type	string	Its label, from the first read when the schema is preloaded
A composite type	string	Its text form
A domain	Its base type
A declared lookup (.Lookup(...))	ArxEntityReference	Name from the referenced table's .DisplayName(...)
A selection set column	Its stored code	entity.GetSelectionSet(column, set, catalog) gives the option
NULL	null	The attribute is present, with a null value

RealCase1_EveryDataTypeReadBack writes one row of every type with Create and prints each value's .NET type as it reads back.