Add conditional check for sqlpp23 alias creation

[bmarques1995]

Check if target sqlpp23::sqlpp23 exists before creating alias. this is important if you need to recreate the cmake target

[MeanSquaredError]

I have a couple of questions about this PR:

1. Where would the existing target sqlpp23::sqlpp23 come from?

2. The generated CMake targets file does not check for the existence of the connector-specific targets (sqlpp23::sqlite3, sqlpp23::mysql, sqlpp23::postgresql, etc) before creating these targets so why should we check for sqlpp23::sqlpp23?

[bmarques1995]

I have a couple of questions about this PR:

1. Where would the existing target sqlpp23::sqlpp23 come from?
2. The generated CMake targets file does not check for the existence of the connector-specific targets (sqlpp23::sqlite3, sqlpp23::mysql, sqlpp23::postgresql, etc) before creating these targets so why should we check for sqlpp23::sqlpp23?

for the first question, I used the target provided by the project (at cmake/configs/Sqlpp23Config.cmake‎)
for the second question, is a weird behavior of cmake, if you rerun the cmake, it tries to create another alias, and this causes a bug.

[MeanSquaredError]

for the first question, I used the target provided by the project (at cmake/configs/Sqlpp23Config.cmake‎)

Which target did you use, was it sqlpp23::sqlpp23 ? Ideally it shouldn't cause problems the way it is now.
Did using that target cause any problems? If yes, then can you provide a minimal reproducible example, which allows us to reproduce the problem?

for the second question, is a weird behavior of cmake, if you rerun the cmake, it tries to create another alias, and this causes a bug.

Again, can you provide the minimal reproducible example?

Actually I cannot imagine how and why it would try to create a second alias. I'd like to examine the problem in more detail, because the proposed fix in your PR seems to be masking some other bug.

[MeanSquaredError]

I tried to reproduce the problem, that your PR tries to fix, with the connection pool example. The connection pool example needed a few minor fixes (see the other PR that I just submitted), but otherwise it worked fine.

I tried modifying its CMakeLists.txt and replaced the sqlpp23::core target with sqlpp23::sqlpp23 and it compiled just fine.
Running cmake -B build multiple times works fine, just as expected. Running cmake --build build multiple times also works well. See the console log below:

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake -B build 
-- The CXX compiler identification is GNU 15.2.1
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Found PostgreSQL: /usr/lib64/libpq.so (found version "18.0")
-- Configuring done (0.5s)
-- Generating done (0.0s)
-- Build files have been written to: /usr/local/projects/github/sqlpp23/examples/connection_pool/build
root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake -B build 
-- Configuring done (0.0s)
-- Generating done (0.0s)
-- Build files have been written to: /usr/local/projects/github/sqlpp23/examples/connection_pool/build
root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake --build build
[ 25%] Building CXX object CMakeFiles/connection_pool.dir/src/db_connection.cpp.o
[ 50%] Building CXX object CMakeFiles/connection_pool.dir/src/db_global.cpp.o
[ 75%] Building CXX object CMakeFiles/connection_pool.dir/src/main.cpp.o
[100%] Linking CXX executable connection_pool
[100%] Built target connection_pool
root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake --build build
[100%] Built target connection_pool
root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# 

So for me everything works correctly, just as expected. As I said before, I really want to see your minimal reproducible example, because I am unable to reproduce the error on my machine. Just for the record, I am using CMake 4.2.1

[bmarques1995]

I tried to reproduce the problem, that your PR tries to fix, with the connection pool example. The connection pool example needed a few minor fixes (see the other PR that I just submitted), but otherwise it worked fine.

I tried modifying its CMakeLists.txt and replaced the sqlpp23::core target with sqlpp23::core and it compiled just fine.

Running cmake -B build multiple times works fine, just as expected. Running cmake --build build multiple times also works well. See the console log below:

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake -B build 

-- The CXX compiler identification is GNU 15.2.1

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Check for working CXX compiler: /usr/bin/c++ - skipped

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success

-- Found Threads: TRUE

-- Found PostgreSQL: /usr/lib64/libpq.so (found version "18.0")

-- Configuring done (0.5s)

-- Generating done (0.0s)

-- Build files have been written to: /usr/local/projects/github/sqlpp23/examples/connection_pool/build

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake -B build 

-- Configuring done (0.0s)

-- Generating done (0.0s)

-- Build files have been written to: /usr/local/projects/github/sqlpp23/examples/connection_pool/build

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake --build build

[ 25%] Building CXX object CMakeFiles/connection_pool.dir/src/db_connection.cpp.o

[ 50%] Building CXX object CMakeFiles/connection_pool.dir/src/db_global.cpp.o

[ 75%] Building CXX object CMakeFiles/connection_pool.dir/src/main.cpp.o

[100%] Linking CXX executable connection_pool

[100%] Built target connection_pool

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# cmake --build build

[100%] Built target connection_pool

root@fedora:/usr/local/projects/github/sqlpp23/examples/connection_pool# 

So for me everything works correctly, just as expected. As I said before, I really want to see your minimal reproducible example, because I am unable to reproduce the error on my machine. Just for the record, I am using CMake 4.2.1

I will send a minimum example later

[rbock]

Thanks for the discussion (especially since I am not a CMake expert at all)!

I suggest to create an issue to discuss what's currently wrong.

[MeanSquaredError]

I suggest to create an issue to discuss what's currently wrong.

That makes sense indeed. I don't quite understand what is the error that bmarques1995 gets. From his explanation it seems that there is an attempt to define the target sqlpp23::sqlpp23 a second time and that causes the error. I don't quite see how such a redefinition could happen under normal circumstances, but it is quite possible that I misunderstand his explanation. Or there could be a bug in CMake, or a bug in sqlpp23's CMake scripts or a bug in his CMakeLists.txt that he has written, or something else.

That's why I agree that it makes sense for @bmarques1995 to open an issue and provide the error message from CMake that he gets, ideally coupled with a minimal reproducible example.