Java: Views and Projections#1916
Merged
Merged
Conversation
MattSchur
commented
Jun 12, 2025
MattSchur
commented
Jun 12, 2025
Contributor
|
Overall, LGTM. It is nice that we explain this stuff. |
Contributor
|
@MattSchur Are all comments addressed and can we review and merge? |
agoerler
reviewed
Jul 3, 2025
Comment on lines
+230
to
+232
| ::: tip Prefer simple views | ||
| Prefer creating multiple simple views, each tailored to a specific use case, rather than a single complex view that tries to address multiple use cases simultaneously. | ||
| ::: |
Contributor
There was a problem hiding this comment.
I think this rather belongs to the best practices
|
|
||
| To add or update CDS views without redeploying the database schema, annotate them with [@cds.persistence.skip](../../guides/databases#cds-persistence-skip). This tells the CDS compiler to skip generating database views for these CDS views, and the CAP Java runtime resolves them dynamically on each request. | ||
|
|
||
| Runtime views must be simple [projections](../../cds/cdl#as-projection-on), not using *aggregations*, *join*, *union* or *subqueries* in the *from* clause, but may have a *where* condition if they are only used to read. On write, the restrictions for [write through views](#updatable-views) apply in the same way as for standard CDS views. However, if a runtime view cannot be resolved, a fallback to database views is not possible, and the statement fails with an error. |
Contributor
There was a problem hiding this comment.
Runtime views may use only CDS QL, which is supported by the CAP Java runtime. Joins and unions are not supported. We have more restrictions in the "resolve" mode. The "cte" mode is more powerful.
Contributor
|
Maybe an overview table would be helpful to list which "features" can be used with
|
Co-authored-by: Adrian Görler <adrian.goerler@sap.com>
agoerler
reviewed
Jul 3, 2025
| ::: warning Avoid selecting to-many Associations | ||
| Do not use [*to-many associations*](../../cds/cdl#to-many-associations) in the select clause of CDS views. This blocks write operations and may cause performance issues due to record duplication on read. | ||
| ::: tip Prefer simple views | ||
| Prefer creating multiple simple views, each tailored to a specific use case, rather than a single complex view that tries to address multiple use cases simultaneously. |
Contributor
There was a problem hiding this comment.
agoerler
reviewed
Jul 3, 2025
Contributor
agoerler
left a comment
agoerler
left a comment
There was a problem hiding this comment.
Looks good to me. Please consider to add some suggestions to https://pages.github.tools.sap/cap/docs/about/best-practices#best-practices-by-cap
(in a different PR)
agoerler
approved these changes
Jul 3, 2025
Contributor
Author
@renejeglinsky Yes, please review and merge |
Comment on lines
+248
to
+249
| ::: warning Avoid Composition Definitions in Views | ||
| Avoid [defining](../../cds/cql#association-definitions) new *compositions* in CDS views and prefer *associations* instead, as [deep write](#updatable-views) and [cascading delete](#delete-via-view) are only supported for compositions in persistence entities. |
Contributor
There was a problem hiding this comment.
Suggested change
| ::: warning Avoid Composition Definitions in Views | |
| Avoid [defining](../../cds/cql#association-definitions) new *compositions* in CDS views and prefer *associations* instead, as [deep write](#updatable-views) and [cascading delete](#delete-via-view) are only supported for compositions in persistence entities. | |
| ::: warning Avoid composition definitions in views | |
| Do not [define](../../cds/cql#association-definitions) *compositions* in CDS views and prefer *associations* instead, to avoid [cascading over associations](#cascading-over-associations). |
Contributor
Author
There was a problem hiding this comment.
It's not about avoiding cascading over associations but deep write and cascade delete are not supported by the runtime for such compositions and would need to be handled by custom code.
MattSchur
commented
Jul 3, 2025
![github-actions[bot]](https://avatars.githubusercontent.com/in/15368?s=60&v=4){kind=small}
MattSchur
commented
Jul 3, 2025
…into write-through-views
renejeglinsky
approved these changes
Jul 4, 2025
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
6 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Introduces "Views and Projections" section with
and documents some rules for write via path expressions in views.
Also shortens some headers to improve the readability in the navigation bar.