How manipulate layers with functions of databases

Aplies

Hello,

I'm trying to get layers from spatial databases but I don't understand how this works.
Indeed, we never get a layer structure with the functions. We manipulate "GM_DB_TableList_t32" structure and I don't know how use this to get a layer with the other functions of SDK.

Best regards,

Tristan C.

bmg_bob

Hello,

You can get a layer for a database table using GM_LoadLayerListEx:

GM_DLL_EXPORTED GM_Error_t32 __stdcall GM_LoadLayerListEx
    ( 
    const char*             aFilename,
    GM_LayerHandle_t32**    aLayerList,
    uint32*                 aNumLoadedLayers,
    GM_LoadFlags_t32        aLoadFlags,
    const char*             aExtraLoadOptions
    );

Pass the file name of the database in the aFileName parameter. (If you are connecting to a spatial database on a server, you will need to create a connection string using the GM_DBMakeConnectionString function, then pass the connection string in the aFileName parameter.) Pass the name of the table you want to read in the aExtraLoadOptions parameter.

Here is a snippet from the GMDLL_Tester sample program. In the snippet, we start with the aFileName value. If that variable contains the name of a database file (or connection string) we get the list of tables from the database and choose the first table. If you want to allow your user to choose a table name, you will need to a UI for that.

GM_Error_t32 theErr = GM_Error_None;

// Load as a database table
std::string theTableName;
if ( GM_DBIsDatabaseFile( aFilename ) )
{
    // Get the list of tables to load
    GM_DB_TableList_t32 theTableList = NULL;
    theErr = GM_DBSelectTable( &theTableList, aFilename );
    if ( GM_Error_None == theErr )
    {
        // If any tables were selected, add them to the load string
        uint32 theCount = 0;
        theErr = GM_DBTableList_GetCount( &theCount, theTableList );
        if ( theCount > 0 )
        {
            // For the purposes of this example, only load the first table in the list.
            char theTempTableName[_MAX_PATH];
            theErr = GM_DBTableList_GetTableName( theTempTableName, 0, theTableList );
            theTableName = theTempTableName;
        }

        // Free the table list
        GM_DBTableList_Free( &theTableList );
        theTableList = NULL;
    }
}

// Load the layer
GM_LayerHandle_t32* theLayerHandleList = NULL;
uint32 theNumLayersLoaded = 0;
theErr = GM_LoadLayerListEx
(
    aFilename, &theLayerHandleList, &theNumLayersLoaded, aLoadFlags, theTableName.c_str()
);

Once you have the layer handle list, you can access the data in the layers the same as any other layer type.

I hope this helps.

Cheers,

Bob

Aplies

Thanks for your answer helpful.
It's very simple actually.

Best regards,

Tristan C.

Aplies

Hello,

I have another problem. I can't connect to a spatial database Oracle 10.2 .
I get a connection string with GM_DBMakeConnectionString, then I try GM_DBTestConnection with this string but it displays :
"Database connection failed : in <unamed>"
I verified the connection between my computer and the database with the client of Oracle system, and its good. Its just with the SDK.

Code to create string connection:

GlobalMapperDLL.GM_DBConnectionParms_t connectionParameters = new GlobalMapperDLL.GM_DBConnectionParms_t();
connectionParameters.mConnectionName = "ConnectionBDD";
connectionParameters.mDbType = GlobalMapperDLL.GM_db_type_t8.GM_DB_TYPE_ORACLE;
connectionParameters.mServer = server;
connectionParameters.mPort = port;
connectionParameters.mDbName = database;
connectionParameters.mUserName = user;
connectionParameters.mPassword = password;

// Allocate a large buffer
IntPtr connectionStringPointer = Marshal.AllocCoTaskMem(1024);

LastGMError = GlobalMapperDLL.GM_DBMakeConnectionString(connectionStringPointer, (uint)1024, ref connectionParameters);

if (LastGMError == GlobalMapperDLL.GM_Error_t32.GM_Error_None)
{
// Copy the filename to our own string and free the dynamically allocated buffer
string connectionString = Marshal.PtrToStringAnsi(connectionStringPointer);
Marshal.FreeCoTaskMem(connectionStringPointer);
return connectionString;
}

Best regards,

Tristan C.

Aplies

I tried too several implementation for GM_DBConnectionParms_t structure in C#, but it doesn't work :

public struct GM_DBConnectionParms_t
{
public GM_db_type_t8 mDbType;
public IntPtr mConnectionName;
public IntPtr mServer;
public IntPtr mPort;
public IntPtr mDbName;
public IntPtr mUserName;
public IntPtr mPassword;
} ;

public struct GM_DBConnectionParms_t
{
public GM_db_type_t8 mDbType;
public String mConnectionName;
public String mServer;
public String mPort;
public String mDbName;
public String mUserName;
public String mPassword;
} ;

Best regards,

Tristan C.

Aplies

Actually, my connection string is good :

"<gm_conn_str>:name=X,type=2,host=X.X.X.X,port=X,database=X,user=X,password=X"

Its just the function GM_DBTestConnection which returns an error.

Best regards,

Tristan C.