What are Transaction Groups? They allow you to create simple bi-directional links between your PLCs and databases. With Transaction Groups you can perform tasks such as database to OPC synchronization, recipe management, and historical data logging.

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[00:00] Transaction Groups are available in ignition, through the SQL Bridge Module. They are objects that map data in ignition to and from a database. With every execution cycle, they can perform actions such as storing OPC data to a database table, or writing database table data to OPC data points. A variety of group types, item types, and configuration options means that Transaction Groups are versatile and have a wide range of configuration. We will go over some of the group types and item types in later videos, but for now let's familiarize ourselves with the Transaction Group basics. When the SQL Bridge Module is installed, you will see a new node, in the designer Project Browser for Transaction Groups. When you create a new group, it is only a part of the current project that you're editing. Groups are designed and modified in the designer, on a per-project basis. But, they execute on the gateway. Once they are started, groups will run indefinitely, as long as the gateway is in an active state.

[01:04] Here in the designer, we see the Transaction Group design space. Here, we can create new Transaction Groups and we can also see a list of the recently modified groups. I have one already created named myGroup, so I will double click on it to see its configuration. The Transaction Group design space will allow users to control the group state. It can be enabled, disabled or paused. Currently, myGroup is disabled. If I choose to enable it like so, this change will not take effect until the project is saved. This is true for any configuration change for any Transaction Group. The group's last safe configuration will always be respected, until a new change is physically made and saved. On the bottom, you have two tabs available, to view the current group status, and any events associated with the group itself. The Status tab will show metrics such as total executions, failed executions, while the events tab will show any messages related to the group's state, such as when the group was started, or if the group started in an error state.

[02:04] If I enable the group and save my configuration changes, notice how I've began to see live status information. Similarly, go into the Events tab. We'll see that the group changed to a running state. There are several types of groups that can accomplish different goals. All group types, however, follow common principles. Once a group has started, it will execute on a timer or schedule. Groups also contain data items, which can be OPC items, configure tags, expressions, or even SQL queries in some instances. Expression item execution can be trigger- dependent if defined in the Triggered Expression Items list. Expressions can also ignore a trigger altogether, if defined in the Run Always Expression Items list. Depending on the group type, items can be mapped one directionally or bidirectionally, meaning that data can flow from OPC to a database, a database to OPC, or it can flow in both directions.

[03:04] What I mean by both directions, is that the database will be monitored and when data changes on one side or the other, it will automatically be written to the other side to maintain data synchronization. Transaction Groups can use several different trigger mechanisms, which in conjunction with the timer or schedule, can specifically dictate when the group should execute. When the group is finished running, success or failure can be communicated back to other tasks through handshake mechanisms. The additional videos in this series, we'll dive deeply into each of these features and provide examples of how they might be useful. In short, bidirectional data synchronization between the database and OPC, flexible triggering of group execution and the ability to modify groups with minimal to no downtime, makes them a key component to many ignition projects.

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