---
title: Retrieve a single application error
summary: Loads exactly one App_Error row into a clsAppError object by sequence number.
status: draft
owner: SAIF Doc Gen
last_reviewed: 2026-07-30
library: SAIF.Application.LogView
reference_type: package
operation_id: OP-LV-02
trigger: Caller invokes clsAppError.GetAppError with a sequence number
---

# Retrieve a single application error

`clsAppError.GetAppError` retrieves one error record by its sequence number through the standard BOF single-object retrieve lifecycle. The library provides no application-layer criteria filtering beyond the key — result-count validation happens entirely in `AfterRetrieve`.

| Field | Value |
| --- | --- |
| **Operation ID** | OP-LV-02 |
| **Trigger** | Caller calls `clsAppError.GetAppError(inDataportal, inAppErrorSeqNum)` |
| **Inputs** | `IDataPortalInfo`, `AppErrorSeqNum` |
| **Outputs** | Populated `clsAppError` object on success; an unhandled `ApplicationException("Invalid Results")` when the row count is not exactly one |
| **Primary components** | `clsAppError.GetAppError`, `clsAppError.BeforeRetrieve`, `clsAppError.AfterRetrieve` |
| **Entry point** | `Application\SAIF.Application.LogView\clsAppError.vb` |

## Steps

1. **Build criteria and dispatch the retrieve.** `GetAppError` constructs a `clsAppError.Criteria(inDataportal, inAppErrorSeqNum)` and calls `inDataportal.DataAccessLayer.RetrieveObject(...)`, which drives the BOF retrieve lifecycle.
2. **Configure the retrieve request (`BeforeRetrieve`).** A data request is built with `SQLStatement = MyCriteria.RetrieveSQL` and the parameter `@AppErrorSeqNum` bound from the criteria's `AppErrorSeqNum`, targeting [App_Error](../database-tables.md#app_error). The single-object `RetrieveSQL` property on `clsAppError.Criteria` is a blank (single-space) string in source — there is no executable single-object SELECT statement defined in this library, so the actual retrieval SQL is not documented here.**
3. **Evaluate the result (`AfterRetrieve`).**
   - If the result set contains exactly one row: call `Fill(Results(0))` to populate every field (`DeletedFlag`, `AppErrorSeqNum`, `AppName`, `Environment`, `ErrorDate`, `ErrorInfo`, `ErrorSource`, `MachineName`, `PageName`, `StateInfo`, `UserName`) from the row, then `MarkOld()` ([BR-005](../business-rules.md#br-005-single-object-retrieval-requires-exactly-one-row)).
     - On failure: throw `ApplicationException("Invalid Results")`. This is an unhandled exception, not a broken-rule collection entry, so the caller must catch it explicitly.
4. **Return the populated object.** `AfterRetrieve` returns `Me`, which the BOF pipeline surfaces back through `GetAppError` as the retrieved `clsAppError`.

## Process flow

The following diagram visualizes the single-object retrieve-and-validate flow.

```mermaid
flowchart TD
	Start([Caller calls GetAppError]) --> Build[Build Criteria with AppErrorSeqNum]
	Build --> Retrieve[BeforeRetrieve: bind @AppErrorSeqNum]
	Retrieve --> Exec[Execute retrieve request]
	Exec --> Count{Result count = 1?}
	Count -->|Yes| Fill[Fill object fields, MarkOld]
	Count -->|No| Throw([Throw ApplicationException<br>Invalid Results])
	Fill --> Done([Populated clsAppError returned])
```

## Failure and edge-case behavior

- The single-object `RetrieveSQL` in `clsAppError.Criteria` is a blank placeholder string, so this retrieve path has no documented executable SQL text in this library; the underlying query behavior cannot be confirmed from source.**
- A zero-row match (no such `AppErrorSeqNum`) and a multi-row match are both treated identically as an `ApplicationException("Invalid Results")` ([BR-005](../business-rules.md#br-005-single-object-retrieval-requires-exactly-one-row)) — the exception message does not distinguish the two cases.
- Because the exception is thrown rather than returned as a broken rule, callers must wrap `GetAppError` in exception handling rather than checking `IsValid`.*

## Related documentation
- [Operations and processes](../operations-processes.md)
- [Business rules](../business-rules.md)
- [Database tables](../database-tables.md)

> **Note:** Statements marked with `*` were inferred from code structure, naming
> conventions, or contextual evidence where direct confirmation was not available
> in source artifacts. Statements marked with `**` could not be confirmed; treat
> as unknown until verified.

## Sources
- `Application\SAIF.Application.LogView\clsAppError.vb`