Add migration commands for SQLite; not PGSql

cmake/scripts/cppbessotDbActionTargetResolution.cmake

@@ -0,0 +1,50 @@
+cmake_minimum_required(VERSION 3.16)
+
+function(cppbessot_db_action_target_upper out_var db_target)
+  string(TOUPPER "${db_target}" _upper)
+  set(${out_var} "${_upper}" PARENT_SCOPE)
+endfunction()
+
+function(cppbessot_db_action_resolve_backend_for_target
+    out_backend
+    out_sqlite_path
+    out_pgsql_connstr
+    db_target)
+  cppbessot_db_action_validate_db_target("${db_target}")
+  cppbessot_db_action_target_upper(_target_upper "${db_target}")
+
+  set(_sqlite_var "CPPBESSOT_DB_SQLITE_${_target_upper}_PATH")
+  set(_pgsql_var "CPPBESSOT_DB_PGSQL_${_target_upper}_CONNSTR")
+
+  set(_has_sqlite FALSE)
+  set(_has_pgsql FALSE)
+
+  if(DEFINED ${_sqlite_var} AND NOT "${${_sqlite_var}}" STREQUAL "")
+    set(_has_sqlite TRUE)
+  endif()
+
+  if(DEFINED ${_pgsql_var} AND NOT "${${_pgsql_var}}" STREQUAL "")
+    set(_has_pgsql TRUE)
+  endif()
+
+  if(_has_sqlite AND _has_pgsql)
+    message(FATAL_ERROR
+      "DB target `${db_target}` is ambiguous: both `${_sqlite_var}` and `${_pgsql_var}` are set.")
+  endif()
+
+  if(NOT _has_sqlite AND NOT _has_pgsql)
+    message(FATAL_ERROR
+      "DB target `${db_target}` is not mapped: set exactly one of `${_sqlite_var}` or `${_pgsql_var}`.")
+  endif()
+
+  if(_has_sqlite)
+    set(${out_backend} "sqlite" PARENT_SCOPE)
+    set(${out_sqlite_path} "${${_sqlite_var}}" PARENT_SCOPE)
+    set(${out_pgsql_connstr} "" PARENT_SCOPE)
+    return()
+  endif()
+
+  set(${out_backend} "postgre" PARENT_SCOPE)
+  set(${out_sqlite_path} "" PARENT_SCOPE)
+  set(${out_pgsql_connstr} "${${_pgsql_var}}" PARENT_SCOPE)
+endfunction()