100 lines
3.3 KiB
Markdown
100 lines
3.3 KiB
Markdown
+++
|
|
title = "Singleton Table"
|
|
weight = 1110
|
|
+++
|
|
## Singleton Table
|
|
|
|
_By Elly Nkya at Microsoft Development Center Copenhagen_
|
|
|
|
## [![ ][image0]][anchor0]
|
|
|
|
_
|
|
_
|
|
|
|
**Problem**: The developer needs to define a single record that can contain a set of rules and behavior (optional, mandatory, or defaulting mechanisms), that apply to a functionality, and can be configured by a user.
|
|
|
|
****
|
|
|
|
**Forces**
|
|
|
|
* You want a central place to define the address and logo of your company (see Company Information table).
|
|
* You want to define the no. series that should be used for your sales documents (see Sales & Receivables Setup table).
|
|
* You want to know whether your sales documents should be archived (see Sales & Receivables Setup table).
|
|
* You want to define the rounding accuracy your system should (see General Ledger Setup table).
|
|
|
|
**Solution:** Define a single record that can contain a set of rules and behavior (optional, mandatory, or defaulting mechanisms), that apply to a functionality, and can be configured by a user.
|
|
|
|
In a functionality that is large enough (such as sales, inventory, fixed) you may want to define a global set of rules, that are configurable by the user.
|
|
|
|
**Implementation**
|
|
|
|
**1\. Define: **Create a Setup Table with Dummy a Primary Key. Typically with type Code=10\. Then add fields to define the global rules.
|
|
|
|
**2\. Instantiate: **Place the instantiation code in a central place where it is guaranteed to be invoked before the functionality uses it. This is done in Codeunit 2\.
|
|
|
|
**3\. Enforce: **Give the user access to the record so that he can change the default setup, by creating a Card page. On the page, enforce the singleton to prevent deletion of the record or insertion of a new record
|
|
|
|
**4\. Use: **Access the rule in code and use it
|
|
|
|
****
|
|
|
|
**NAV Usages**
|
|
|
|
Rounding rules for Unit-Amounts and Amounts are implemented using the Singleton pattern.
|
|
|
|
**1\. Define:** The General Ledger Setup is used for this.
|
|
|
|
**2\. Instantiate:** In codeunit 2, the following code is invoked
|
|
|
|
WITH GLSetup DO
|
|
IF NOT FINDFIRST THEN BEGIN
|
|
INIT;
|
|
INSERT;
|
|
END;
|
|
|
|
**3\. Enforce:** On the General Ledger Setup. The following properties are setup:
|
|
|
|
DeleteAllowed=false,
|
|
InsertAllowed=false
|
|
|
|
**4\. Use:** Access the rounding rules are used
|
|
|
|
...
|
|
GLSetup.GET;
|
|
UnitCostCurrency := ROUND(...,GLSetup."Unit-Amount Rounding Precision");
|
|
...
|
|
|
|
Or if accessing the rule multiple times and performance is a consideration, use lazy instantiation:
|
|
|
|
...
|
|
GetGLSetup;
|
|
UnitCostCurrency := ROUND(...,GLSetup."Unit-Amount Rounding Precision");
|
|
...
|
|
|
|
LOCAL GetGLSetup()
|
|
IF NOT GLSetupRead THEN
|
|
GLSetup.GET;
|
|
GLSetupRead := TRUE;
|
|
|
|
**Related topics**
|
|
|
|
[Singleton design pattern][anchor1].
|
|
|
|
The **Singleton Table** has two established applications in Dynamics NAV:
|
|
|
|
1. [**Setup Tables**][anchor2] -- which are commonly storing user setup data in NAV,
|
|
2. **Cue Tables** -- used to calculate values for the visual representation of Cues on the NAV role center pages.
|
|
|
|
YouTube Video of NAV Singleton:
|
|
|
|
[watch?v=aQPu s9FkYI&list=PLhZ3P LY7CqmVszuvtJLujFyHpsVN0Uw&index=13][anchor3]
|
|
|
|
|
|
|
|
[anchor0]: 5554.Singleton-Table.png
|
|
[anchor1]: https://en.wikipedia.org/wiki/Singleton_pattern
|
|
[anchor2]: /nav/w/designpatterns/76.setup-table
|
|
[anchor3]: https://www.youtube.com/watch?v=aQPu-s9FkYI&list=PLhZ3P-LY7CqmVszuvtJLujFyHpsVN0U_w&index=13
|
|
|
|
|
|
[image0]: 5554.Singleton-Table.png
|