**Source URL:** https://general.veevavault.dev/vault-sdk/entry-points/triggers/data-availability.md # Data Availability When processing a request, the System performs the following sequence of steps: 1. Evaluative field dependencies: [Field dependencies](https://platform.veevavault.help/en/gr/2617) are UI-only and are validated before triggers are fired. If Vault Java SDK then changes data, field dependencies are not re-evaluated. 2. Execute `BEFORE` [Action Triggers](https://platform.veevavault.help/en/gr/811001). 3. Execute `BEFORE` triggers. 4. Write record changes to database. 5. Update changes in VQL index. 6. Execute `AFTER` [Action Triggers](https://platform.veevavault.help/en/gr/811001). 7. Execute `AFTER` triggers. The data available in `BEFORE` and `AFTER` event triggers depends on the operations (`INSERT`, `UPDATE`, and `DELETE`). For example, in an `INSERT` operation, you cannot get old or existing values because a new record is being inserted. Similarly, setting a field value only makes sense in the `BEFORE` event in `INSERT` and `UPDATE` operations. It doesn't make sense to set field value after it has been persisted or in a `DELETE` operation. The following chart illustrates when you can get or set field values.

	getNew()		getOld()
	getValue	setValue	getValue	setValue
BEFORE_INSERT	✓	✓
AFTER_INSERT	✓
BEFORE_UPDATE	✓	✓	✓
AFTER_UPDATE	✓		✓
BEFORE_DELETE			✓
AFTER_DELETE			✓

### Query vs RecordService#readRecord {#query-vs-recordservicereadrecord} As illustrated above, `BEFORE` triggers can change field values, but these values are not persisted to the database and not updated in the VQL index yet. In this case, using the `QueryService` to retrieve a record being modified by a trigger will only return the old (existing) values. In order to get the values set by a trigger inside a transaction, you must use the `RecordService#readRecord` method. However, this method generally uses more memory. It is only recommended when you need to get field values modified by multiple triggers in a single transaction. Otherwise, we recommend `QueryService` to retrieve record data. Because `AFTER` triggers happen after database updates and VQL indexing, you can use `QueryService` to retrieve both old and new values. ## System Populated Fields {#system-populated-fields} Certain field types in Vault have values set by the System. For example: * [Lookup Fields](https://platform.veevavault.help/en/gr/34072) are read-only fields that the System populates with the "Lookup Source Field" value. * [Document Reference Fields](https://platform.veevavault.help/en/gr/35045) have two fields (bound and unbound), and when configured to reference the "Latest Version", the bound field becomes read-only, and the System populates it with the latest document version value. In general, the System populates field values after the `BEFORE` event. Because these field values are set by the System, the changes are not reflected in the `BEFORE` event. For example, `getNew()` and `getOld()` will return the same existing value or null accordingly. However, the `AFTER` event will return the new value set by the System in `getNew()` and the existing value in `getOld()`. For example, when creating a new document, documents using document auto-naming will have a null value for name in `BEFORE_INSERT` events. In addition, because System-initiated requests do not fire triggers, triggers will not fire when the System updates a System-populated field. If your trigger updates a document reference field, you must set the *Document Version Reference* to *Specific Version*. Learn more in [Vault Help](https://platform.veevavault.help/en/gr/35045). --- **Previous:** [Execution Flow](/vault-sdk/entry-points/triggers/execution-flow) **Next:** [Performance Considerations](/vault-sdk/entry-points/triggers/performance-considerations)