Links are the things that connect project items to each other. If Tool is the heart of a DAG, then links are the veins that connect the heart to other vital organs.
Creating a new link between items is simple. First you need to select any of the connector slots on the item where you want the link to originate form. Then select any connector slot on the item that you want to connect to. There are no limitations for how many links one connector slot can have. Like items, links can also have properties, depending on the types of items that they are connecting. When a link is selected, these properties can be modified in the Properties dock widget.
The small bubble icons in a link represent the state of the link's properties. When an icon is blue, the corresponding selection is active in the Properties dock widget.
Below is an example of what the Properties dock widget can look like when a link originating from a Data Store is selected:
DB resource filters is divided into Scenario and Tool filters. With the scenario filters, you can select which scenarios to include in the execution. The Tool filter lets you choose which tools specified in the database are active. The Check new filters automatically option allows you to choose whether new Scenario and Tool filters added to the database should be automatically selected in this specific link. Filter validation allows you to force that at least one Scenario and/or Tool filter is selected at all times in that specific link.
In the image below, the selected link ends in a Data Store. Because of this, the available selections in Properties differ from the previous image.
Now the link has no filters, but the write index and other various database related options become available.
Write index controls which items write to the database first. Smaller indices take precedence over larger ones while items with the same index write in an undefined order.
Purge before writing option purges the target Data Store before write operations. Click on Settings... to set up which items to purge.
Warning
This purge has no undo available.
Use memory DB for Tool execution allows using a temporary in-memory database while executing a Tool which may speed up execution if the Tool accesses the database a lot.
When the source item may provide output files, the Pack CSV files (as datapackage.json) option becomes enabled. This option may be handy when an item provides a lot of CSV files that e.g. need to imported into a Data Store. Checking this options does two things:
- A
datapackage.jsonfile is created in the common parent directory of all CSV files the source item provides. This file defines a datapackage that consists of the CSV files. - The destination item receives only the
datapackage.jsonfile instead of any CSV files from the source item.
See the datapackage specification for more information on datapackages.