- Creating a link
- Owner file and member file
- Referential integrity
The links are used to link the date files described in an analysis between themselves.
Several types of links are available. For more details, see Types of links
Reminder: The "LDM" and "Analysis" terms are indifferently used to define the structure of database associated with a project.
To create a link:
- On the "Analysis" tab, in the "Creation" group, click "New link". The mouse cursor turns into a pen.
- Click the two data files that must be linked. The link description wizard opens automatically.
- To define the cardinalities between the two files:
- select the desired cardinalities (0, 1; 1, 1; 0, N; 1, N).
- answer the questions. The cardinalities will be automatically updated.
- To define the advanced cardinalities, check "Display advanced cardinalities" and answer the questions.
- Specify the link caption and briefly describe the purpose of the link. Go to the next step.
- Specify the keys to be linked. Go to the next step.
- Define the integrity rules. These rules ensure data integrity when one of the keys of the relationship is modified or deleted.
- Validate. The link is automatically created.
- For more details on cardinalities, see Cardinalities.
- If the data files to link contain an identical unique composite key (and also contain the items included in the composite key), a link can be performed on this composite key.
Owner file and member file
When there is a link between two data files, there is an owner file and a member file:
- the owner file is the key owner.
- the member file is a member of analysis files containing a copy of key.
To manage the link between two data files, the key of the owner file is copied to the member file.
For example, the key of the "Supplier" file is copied to each record of the "Product" file. Several records in the "Product" file can have the same key as the "Supplier" file:
- the owner file is"Supplier",
- the member file is "Product".
This type of link is represented as follows:
Referential integrity in a database is a set of constraints that maintains consistency of data in a relationship between two data files.
Referential integrity checks that:
- if a record is deleted from the owner file, the corresponding records are also deleted from the member files,
- if a record is added to a member data file, there is a matching record in the owner data file,
- if a record is modified in the owner file, the unique key is not modified,
The referential integrity is checked based on the nature of the link between the data files.
Training (WINDEV): WD Reflexive link
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This example presents the management of a reflexive link with the WLanguage functions.
The following topics are presented in this example:
1/ Fill a control with HFSQL content (automatic management of reflexive link).
2/ Fill by programming.
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