Add method to retrieve all valid srs ids from CRS databases

python/core/conversions.sip

@@ -438,6 +438,53 @@ template <TYPE>
 };
 
 
+%MappedType QList<long>
+{
+%TypeHeaderCode
+#include <QList>
+%End
+
+%ConvertFromTypeCode
+  // Create the list.
+  PyObject *l;
+
+  if ((l = PyList_New(sipCpp->size())) == NULL)
+    return NULL;
+
+  // Set the list elements.
+  QList<long>::iterator it = sipCpp->begin();
+  for (int i = 0; it != sipCpp->end(); ++it, ++i)
+  {
+    PyObject *tobj;
+
+    if ((tobj = PyLong_FromLong(*it)) == NULL)
+    {
+      Py_DECREF(l);
+      return NULL;
+    }
+    PyList_SET_ITEM(l, i, tobj);
+  }
+
+  return l;
+%End
+
+%ConvertToTypeCode
+  // Check the type if that is all that is required.
+  if (sipIsErr == NULL)
+    return PyList_Check(sipPy);
+
+  QList<long> *qlist = new QList<long>;
+
+  for (int i = 0; i < PyList_GET_SIZE(sipPy); ++i)
+  {
+    *qlist << PyLong_AsLong(PyList_GET_ITEM(sipPy, i));
+  }
+
+  *sipCppPtr = qlist;
+  return sipGetState(sipTransferObj);
+%End
+};
+
 %MappedType QList<qint64>
 {
 %TypeHeaderCode

python/core/qgscoordinatereferencesystem.sip

@@ -183,6 +183,8 @@ class QgsCoordinateReferenceSystem
     // TODO QGIS 3: remove theType and always use EPSG code
     QgsCoordinateReferenceSystem( const long theId, CrsType theType = PostgisCrsId );
 
+    static QList< long > validSrsIds();
+
     // static creators
 
     /** Creates a CRS from a given OGC WMS-format Coordinate Reference System string.

src/core/qgscoordinatereferencesystem.cpp

@@ -90,6 +90,66 @@ QgsCoordinateReferenceSystem& QgsCoordinateReferenceSystem::operator=( const Qgs
   return *this;
 }
 
+QList<long> QgsCoordinateReferenceSystem::validSrsIds()
+{
+  QList<long> results;
+  // check both standard & user defined projection databases
+  QStringList dbs = QStringList() <<  QgsApplication::srsDatabaseFilePath() << QgsApplication::qgisUserDatabaseFilePath();
+
+  Q_FOREACH ( const QString& db, dbs )
+  {
+    QFileInfo myInfo( db );
+    if ( !myInfo.exists() )
+    {
+      QgsDebugMsg( "failed : " + db + " does not exist!" );
+      continue;
+    }
+
+    sqlite3 *database = nullptr;
+    const char *tail = nullptr;
+    sqlite3_stmt *statement = nullptr;
+
+    //check the db is available
+    int result = openDatabase( db, &database );
+    if ( result != SQLITE_OK )
+    {
+      QgsDebugMsg( "failed : " + db + " could not be opened!" );
+      continue;
+    }
+
+    QString sql = "select srs_id from tbl_srs";
+    result = sqlite3_prepare( database, sql.toUtf8(),
+                              sql.toUtf8().length(),
+                              &statement, &tail );
+    while ( 1 )
+    {
+      // this one is an infinitive loop, intended to fetch any row
+      int ret = sqlite3_step( statement );
+
+      if ( ret == SQLITE_DONE )
+      {
+        // there are no more rows to fetch - we can stop looping
+        break;
+      }
+
+      if ( ret == SQLITE_ROW )
+      {
+        results.append( sqlite3_column_int( statement, 0 ) );
+      }
+      else
+      {
+        QgsMessageLog::logMessage( QObject::tr( "SQLite error: %2\nSQL: %1" ).arg( sql, sqlite3_errmsg( database ) ), QObject::tr( "SpatiaLite" ) );
+        break;
+      }
+    }
+
+    sqlite3_finalize( statement );
+    sqlite3_close( database );
+  }
+  std::sort( results.begin(), results.end() );
+  return results;
+}
+
 QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::fromOgcWmsCrs( const QString& ogcCrs )
 {
   QgsCoordinateReferenceSystem crs;

src/core/qgscoordinatereferencesystem.h

@@ -236,6 +236,15 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
     //! Assignment operator
     QgsCoordinateReferenceSystem& operator=( const QgsCoordinateReferenceSystem& srs );
 
+    /**
+     * Returns a list of all valid SRS IDs present in the CRS database. Any of the
+     * returned values can be safely passed to fromSrsId() to create a new, valid
+     * QgsCoordinateReferenceSystem object.
+     * @see fromSrsId()
+     * @note added in QGIS 3.0
+     */
+    static QList< long > validSrsIds();
+
     // static creators
 
     /** Creates a CRS from a given OGC WMS-format Coordinate Reference System string.
@@ -274,6 +283,7 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
      * @returns matching CRS, or an invalid CRS if ID could not be found
      * @note added in QGIS 3.0
      * @see createFromSrsId()
+     * @see validSrsIds()
     */
     static QgsCoordinateReferenceSystem fromSrsId( long srsId );
 

tests/src/core/testqgscoordinatereferencesystem.cpp

@@ -73,6 +73,8 @@ class TestQgsCoordinateReferenceSystem: public QObject
     void setValidationHint();
     void hasAxisInverted();
     void createFromProj4Invalid();
+    void validSrsIds();
+
   private:
     void debugPrint( QgsCoordinateReferenceSystem &theCrs );
     // these used by createFromESRIWkt()
@@ -724,5 +726,19 @@ void TestQgsCoordinateReferenceSystem::createFromProj4Invalid()
   QVERIFY( !myCrs.createFromProj4( "+proj=longlat +no_defs" ) );
 }
 
+void TestQgsCoordinateReferenceSystem::validSrsIds()
+{
+  QList< long > ids = QgsCoordinateReferenceSystem::validSrsIds();
+  QVERIFY( ids.contains( 3857 ) );
+  QVERIFY( ids.contains( 28356 ) );
+
+  // check that all returns ids are valid
+  Q_FOREACH ( long id, ids )
+  {
+    QgsCoordinateReferenceSystem c = QgsCoordinateReferenceSystem::fromSrsId( id );
+    QVERIFY( c.isValid() );
+  }
+}
+
 QGSTEST_MAIN( TestQgsCoordinateReferenceSystem )
 #include "testqgscoordinatereferencesystem.moc"