Add custom build step in CMake - c++

Question

I'm trying to add a custom build step in CMake that generates some files. I haven't found a description how it works.
I have an project where source, header & implementation files have to be generated by ODB for C++. ODB takes class headers as arguments and generates source files that I want to use in my project.
Right now I have the following command in my CMakeLists.txt:
add_custom_command(TARGET ${PROJECT_NAME}
PRE_BUILD
COMMAND odb -o /home/david/dev/ --std c++11 -I/home/david/dev/ -d sqlite --generate- query --generate-schema ${PROMOTER_LIB_PREFIX}/entities/person.hpp
DEPENDS ${PROJECT_NAME}
VERBATIM
)
For a file person.hpp ODB should generate person-odb.hxx, person-odb.cxx, person-odb.ixx but the CMake command I''ve used doesn't generate anything. In a terminal this command works fine.
What am I doing wrong?
EDIT: The problem can be solved by adding the following lines:
set(FAKE_TARGET fakeTarget)
add_custom_target(fakeTarget
odb -o /home/david/dev/ --std c++11 -I/home/david/dev/ -d sqlite --generate-query --generate-schema ${PROMOTER_LIB_PREFIX}/entities/person.hpp
)
add_dependencies(${PROJECT_NAME} ${FAKE_TARGET})

Answer 1

For me, with something similar, I just use :
add_custom_command(TARGET ${PROJECT_NAME}
PRE_BUILD
COMMAND odb -o /home/david/dev/ --std c++11 -I/home/david/dev/ -d sqlite --generate- query --generate-schema ${PROMOTER_LIB_PREFIX}/entities/person.hpp
)
We don't use DEPENDS or VERBATIM.
The DEPENDS option specify that the command must be executed only after that the project you gave to this option is built.
EDIT :
Note that the PRE_BUILD option is only supported on Visual Studio 7 or later. For all other generators PRE_BUILD will be treated as PRE_LINK.
Maybe that's why it doesn't work for you.
A work around could be (a bit ugly) :
Create a fake project
Add your custom command on it as POST_BUILD
Make you current project dependent on the fake one

Answer 2

Way I'm using it is:
add_custom_command(
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/gen_icinstrtab.hpp
COMMAND xsltproc --output ${CMAKE_CURRENT_BINARY_DIR}/gen_icinstrtab.hpp ${CMAKE_SOURCE_DIR}/xml/genictabc.xslt ${CMAKE_SOURCE_DIR}/xml/icminstr.xml
)
add_executable(
du4
${CMAKE_CURRENT_BINARY_DIR}/gen_icinstrtab.hpp
.
.
.
)
The key was to add even .hpp files into add_executable block.