X++ Fundamentals: Syntax & CRUD

Welcome to Domain 4 — the heart of MB-500. X++ powers every customisation in D365 Finance and Operations.

Variables and Data Types

Type	Description	Example
int / int64	Integer	int count = 10;
real	Decimal	real price = 29.99;
str	String	str name = "Contoso";
boolean	True/false	boolean active = true;
date / utcdatetime	Date values	date today = systemDateGet();
container	Mixed-type collection	container c = [1, "hello", true];

🎓 Sophie’s first day: “Carl said the biggest surprise is the container type — like a tuple holding any mix. Indexing starts at 1, not 0!”

Containers

container data = [1001, "Contoso", 29.99];
int id   = conPeek(data, 1);    // 1001 (1-based!)
str name = conPeek(data, 2);    // "Contoso"
int size = conLen(data);         // 3
container updated = conIns(data, 2, "NYC"); // new container

💡 Exam tip: Container indexing starts at 1

conPeek(c, 0) causes a runtime error. Containers are 1-based. The exam tests this.

Control Flow

if (custTable.AccountNum == "1001")
    info("Found");
else
    error("Not found");

switch (salesLine.SalesStatus)
{
    case SalesStatus::Backorder: info("Back"); break;
    case SalesStatus::Delivered: info("Done"); break;
}

for (int i = 1; i <= 10; i++)
    info(strFmt("Item %1", i));

🏗️ Vik: “90% of the time you loop with while select, not plain for/while.”

Reading Data — select

CustTable custTable;
select firstOnly custTable where custTable.AccountNum == "1001";
if (custTable)
    info(strFmt("Customer: %1", custTable.Name));

while select

CustTable custTable;
while select custTable where custTable.Blocked == CustVendorBlocked::No
{
    info(strFmt("%1 - %2", custTable.AccountNum, custTable.Name));
}

Joins and aggregates

CustTable custTable;
CustTrans custTrans;
while select custTable
    join custTrans where custTrans.AccountNum == custTable.AccountNum
{
    info(strFmt("%1: %2", custTable.Name, custTrans.Voucher));
}

select count(RecId) from custTable where custTable.Blocked == CustVendorBlocked::No;

select Keywords

Keyword	Purpose
firstOnly	Return one record
order by	Sort results
group by / count / sum	Aggregates
join / outer join	Table joins
exists join / notexists join	Existence filter
forUpdate	Lock for modification

Writing Data — Insert, Update, Delete

// INSERT
CustTable custTable;
ttsBegin;
    custTable.AccountNum = "9001";
    custTable.Name = "New Customer";
    custTable.insert();
ttsCommit;

// UPDATE (forUpdate required!)
ttsBegin;
    select forUpdate custTable where custTable.AccountNum == "9001";
    if (custTable) { custTable.Name = "Updated"; custTable.update(); }
ttsCommit;

// DELETE
ttsBegin;
    select forUpdate custTable where custTable.AccountNum == "9001";
    if (custTable) { custTable.delete(); }
ttsCommit;

Key patterns: ttsBegin/ttsCommit for transactions. forUpdate locks the record. Always check if (buffer) before update/delete.

💡 Exam tip: tts nesting

Transaction scopes nest. Only the outermost ttsCommit commits. Any exception rolls back everything.

Global Functions

Function	Purpose
strFmt("Hello %1", name)	String formatting
conPeek(c, 1) / conLen(c)	Container ops
systemDateGet()	Current date
info() / warning() / error()	Infolog messages
classStr() / tableStr()	Compile-time names

Best Practice Rules

The compiler includes a BP checker — like ESLint for X++.

Rule	Catches	Fix
Missing label	Hardcoded UI strings	Use @SYS labels
Select without where	Unbounded queries	Add where clause
Unused variable	Declared not used	Remove it

👨‍💻 Elena: “Use strFmt for all formatting, not concatenation. Cleaner, faster, translatable.”

Question

select firstOnly vs while select?

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Answer

firstOnly gets one record. while select iterates all matches.

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Question

What does ttsBegin/ttsCommit do?

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Answer

Transaction scope. All modifications atomic — all succeed or roll back.

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Question

What keyword before update()/delete()?

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Answer

forUpdate — locks the record. Without it, runtime error.

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Knowledge Check

Correct X++ to fetch one customer?

Aselect firstOnly custTable where custTable.AccountNum == '1001';BSELECT TOP 1 FROM custTable WHERE AccountNum = '1001';CcustTable.find('1001');Dselect custTable limit 1;

Check Answer

Knowledge Check

Vik updates without forUpdate. What happens?

ARuntime error — record not lockedBCompile errorCUpdate silently succeedsDUpdate silently fails

Check Answer

Knowledge Check

conPeek(data, 0) on a container?

ARuntime error — indexing starts at 1BReturns first elementCReturns nullDCompile error

Check Answer

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Next up: Object-Oriented X++ — classes, inheritance, QueryBuilder, and attributes.