What is DML in Apex and what are its limits?

DML (Data Manipulation Language) is how Apex inserts, updates, deletes, undeletes, and upserts records. Two syntaxes:

Statement form (concise):

apex insert acc; update accList; delete oppList; upsert leads External_Id__c;

Database method form (more options):

apex Database.SaveResult[] results = Database.insert(accList, false); // false = allow partial success

Database methods give you partial-success flag (allOrNone = false) and per-record SaveResult objects with success/error info.

Governor limits:

• 150 DML statements per transaction.
• 10,000 records per DML in sync; higher async.
• Each statement counts as one regardless of record count.

Best practices:

• Bulkify: do one insert listOfX instead of insert x in a loop. Loops with DML inside hit the 150 limit fast.
• Don't mix sObject types in one Database method call — that's a different limit.
• Use upsert with External Id for integrations to avoid duplicate-key issues.

DML inside a loop is the #1 anti-pattern in Apex.