Description

The user has come across various issues with using nested blueprint structs within a data table.
The first issue relates to changing a variable in a child struct and setting it back then saving, causing a compilation error.
The second issue is data from the data table being wiped after deleting the inner-most child struct, and then changing the middle struct's variables.
Licensee has provided repro steps to be used with the attached sample project.

Steps to Reproduce

Steps to Reproduce:

1. Open DT_Example: Note that values for the MiddleStruct (housed inside the row ST_Outer) are populated, or populate them with your own values.
2. Create a new struct anywhere (I'm calling it ST_Inner)
3. Open ST_Middle and change one of the variable types to be ST_Inner.
4. Open ST_Inner and add a variable.
5. Save both.
6. Open ST_Outer and note it has no compilation issues.
7. Change the variable of ST_Inner on ST_Middle to something else, then swap it back.
8. Look at ST_Outer and notice it has a compilation issue that can only be resolved by adding/removing a variable.

This is the first issue we've encountered, and we've had this issue with compiling structs come up in other contexts but this was one of the most consistent. A bigger issue stemming from this follows:
Do all of the above, including fixing ST_Outer's compilation by adding/removing a variable (don't remove the ST_Middle variable)

1. Delete the ST_Inner struct (Force delete).
2. Note that this causes ST_Middle to have a "fallback struct" where ST_Inner once was.
3. Add a variable to ST_Middle. This will generate a warning on the fallback struct.
4. Note that ST_Outer has the same warning on its member variable of ST_Middle.
5. Now no matter what, even after fixing the structs, DT_Example will have all data pertaining to ST_Middle, even data unrelated to ST_inner, wiped.

Again, this issue of data table wiping has been happening in a few different contexts, this is just one which is consistent. The issue has always cropped up related to nested blueprint structs.

Have Comments or More Details?

There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-222101 in the post.

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Unresolved
ComponentUE - Gameplay - Blueprint Compiler
Affects Versions5.45.3
Target Fix5.5
CreatedAug 19, 2024
UpdatedAug 23, 2024
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