Embedded C/C++ Application (Linux/gcc)

Introduction

Now that you've gotten comfortable with creating a database in the How to Create a Schema section, lets build an application that will allow you to read and write to a database.

We recommend getting familiar with some of the concepts and tools that you will be using in this tutorial. We will be covering: interacting with the Transaction File Server (TFS), inserting a row with the function call rdm_dbInsertRow(), and reading rows with the function call rdm_cursorReadRow(). You may also find it useful to read about the DOCROOT as well.

  • The TFS is responsible for safely storing and retrieving objects. It is like a key/value store, but very fast and transactionally safe. The TFS owns and is co-located with the database files.
  • In this example rdm_dbInsertRow() will be used to insert a new row into two of our tables: AUTHOR and BOOK.
  • rdm_cursorReadRow() reads all columns from a row specified by the RDM_CURSOR and places the contents inside of the designated buffer.
  • The DOCROOT is a directory which is designated for holding databases available to a Transaction File Server (TFS). The concept is similar to a web server document root for storing web pages

Prerequisites:

Steps: 

  1. First create a new project folder
    $> mkdir App
  2. Change directories into your project 
    $> cd App
  3. Create a new file and name it bookStore.c 
  4. Change bookStore.c to look like this: 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "rdm.h"
#include "bookStore_structs.h"

/* Write a row to from author and book tables */
static RDM_RETCODE writeARow (RDM_DB db)
{
    RDM_RETCODE rc;
    RDM_TABLE_ID tables[] = {TABLE_BOOK, TABLE_AUTHOR};

    char last_name[13];
    char full_name[35];
    char bookid[14];
    char title[105];
    char price[10];
    RDM_BCD_T dPrice;
    char *inputs[5] = {last_name, full_name, bookid, title, price};
    unsigned int len;
    int ii = 0;

    printf ("ADDING AUTHOR TO DATABASE\nAuthor Last Name:\n");
    fgets (last_name, 13, stdin);
    printf ("Author Full Name:\n");
    fgets (full_name, 35, stdin);
    printf ("ADDING BOOK TO DATABASE\nTitle of Book:\n");
    fgets (title, 105, stdin);
    printf ("Enter id located on book:\n");
    fgets (bookid, 14, stdin);
    printf ("Price:\n");
    fgets (price, 10, stdin);

    /* Remove newline character from fgets */
    while (ii < (sizeof (inputs) / sizeof (inputs[0])))
    {
        len = strlen (inputs[ii]);
        if (inputs[ii][len - 1] == '\n')
        {
            inputs[ii][len - 1] = '\0';
        }
        ii++;
    }

    /* Start an update transaction and lock the table */
    rc = rdm_dbStartUpdate (db, tables, RDM_LEN(tables), NULL, 0, NULL);
    if (rc == sOKAY)
    {
        AUTHOR authInsert; /* Row buffer */
        BOOK bookInsert;   /* Row buffer */

        /* Populate the columns in the AUTHOR Row buffer */
        strcpy (authInsert.LAST_NAME, last_name);
        strcpy (authInsert.FULL_NAME, full_name);
        authInsert._FULL_NAME_has_value = RDM_COL_HAS_VALUE;

        /* Insert a row into the table */
        rc = rdm_dbInsertRow (db, TABLE_AUTHOR, &authInsert, sizeof (authInsert), NULL);

        if (rc == sOKAY)
        {
            /* Convert the string to a binary-coded decimal */
            rdm_bcdFromString (price, &dPrice);

            /* Populate the columns in the BOOK Row buffer */
            strcpy (bookInsert.TITLE, title);
            bookInsert._TITLE_has_value = RDM_COL_HAS_VALUE;
            strcpy (bookInsert.BOOKID, bookid);
            bookInsert.PRICE = dPrice;
            bookInsert._PRICE_has_value = RDM_COL_HAS_VALUE;

            /* Insert a row into the table */
            rc = rdm_dbInsertRow (db, TABLE_BOOK, &bookInsert, sizeof (bookInsert), NULL);
        }
        if (rc == sOKAY)
        {
            /* Commit a transaction */
            printf ("The book %s by %s at a price of $%s was added to the database successfully.\n",
                    title, full_name, price);
            rc = rdm_dbEnd (db);
        }
        else
        {
            /* Abort the transaction */
            fprintf (stderr, "A problem occurred when adding data to the database.\n");
            fprintf (stderr, "Error: %s (%d): %s\n", rdm_retcodeGetName (rc), rc, rdm_retcodeGetDescription (rc));
            rdm_dbEndRollback (db);
        }
    }
    return rc;
}

/* Read rows from author table */
static RDM_RETCODE readRows (RDM_DB db)
{
    RDM_RETCODE rc;
    RDM_TABLE_ID tables[] = {TABLE_AUTHOR};
    AUTHOR authRead;
    RDM_CURSOR cursor = NULL;

    rc = rdm_dbStartRead (db, tables, RDM_LEN(tables), NULL);
    if (rc == sOKAY)
    {
        rc = rdm_dbGetRows (db, TABLE_AUTHOR, &cursor);
        if (rc == sOKAY)
        {
            /* Navigate to the first row in the cursor */
            printf ("Displaying all of the authors in the author table\n");
            rc = rdm_cursorMoveToFirst (cursor);
            while (rc == sOKAY)
            {
                /* Read the row column values */
                rc = rdm_cursorReadRow (cursor, &authRead, sizeof (authRead), NULL);
                if (rc == sOKAY)
                {
                    puts (authRead.LAST_NAME);

                    /* Move to the next row in the cursor */
                    rc = rdm_cursorMoveToNext (cursor);
                }
            }

            /* We expect to break out of the loop with a sENDOFCURSOR code*/
            if (rc == sENDOFCURSOR)
            {
                rc = sOKAY;
            }

            /* Free the cursor allocated in rdm_dbGetRows */
            rdm_cursorFree (cursor);
        }

        /* release the read locks */
        rdm_dbEnd (db);
    }
    return rc;
}

int main (int argc, const char* const* argv)
{
    RDM_RETCODE rc; /* Status/Error Return Code */
    RDM_TFS tfs;    /* TFS Handle */
    RDM_DB db;      /* Database Handle */

    RDM_UNREF(argc);
    RDM_UNREF(argv);

    /* Allocate a TFS Handle */
    rc = rdm_rdmAllocTFS (&tfs);
    if (rc == sOKAY)
    {
        rc = rdm_tfsInitialize (tfs);
        if (rc == sOKAY)
        {
            /* Allocate a database handle */
            rc = rdm_tfsAllocDatabase (tfs, &db);
            if (rc == sOKAY)
            {
                /* Open the database */
                rc = rdm_dbOpen (db, "bookStore", RDM_OPEN_SHARED);
                if (rc == sOKAY)
                {
                    /* Insert a row to database */
                    rc = writeARow (db);
                    if (rc == sOKAY)
                    {
                        /* Read the rows */
                        rc = readRows (db);
                    }
                    rdm_dbClose (db);
                }
                else
                {
                    fprintf (stderr, "\nSorry, can't open bookStore database.\n");
                    fprintf (stderr, "Error: %s (%d): %s\n", rdm_retcodeGetName (rc), rc, rdm_retcodeGetDescription (rc));
                }
                rdm_dbFree (db);
            }
        }
        rdm_tfsFree (tfs);
    }


    return rc == sOKAY ? EXIT_SUCCESS : EXIT_FAILURE;
}
  1. For configure example, we have a pre-written Makefile.am and configure.ac here for you to use. Create the following two files inside of your project:

Makefile.am

The example file below includes all the libraries that will need to be included for this example. The libraries needed will be the libraries referenced by the applications use of the RDM APIs plus all of the dependency libraries which can be determined in the RDM Libraries section of the reference manual.

bin_PROGRAMS = bookStore

AM_CFLAGS = \
    -Wall \
    -I$(RDM_INCDIR) \
    $(RDM_CFLAGS)

AM_LDFLAGS = \
    -L$(RDM_LIBDIR)

bookStore_SOURCES = \
    bookStore.c

bookStore_LDADD = \
    -lrdmrdm \
    -lrdmddl \
    -lrdmtfs_embed \
    -lrdmtx \
    -lrdmpsp \
    -lrdmbase \
    -lpthread \
    -lrt \
    -lm

configure.ac

The RDM_INSTALL_DIR variable in the following may need to be changed to the directory where RDM is installed on your computer.

# initialize the process
AC_INIT([bookStore], [0.01])
# make config headers
AC_CONFIG_HEADERS([config.h])
# init automake
AM_INIT_AUTOMAKE([1.11])
#configure and create "Makefile"
AC_CONFIG_FILES([Makefile])
#find and probe C compiler
AC_PROG_CC

RDM_INSTALL_DIR=/opt/Raima/rdm_enterprise-15.2

RDM_INCDIR="${RDM_INSTALL_DIR}/include"
RDM_LIBDIR="${RDM_INSTALL_DIR}/lib"

#
# RDM Flags
#
AC_SUBST([RDM_CFLAGS])
AC_SUBST([RDM_LDFLAGS])
AC_SUBST([RDM_INCDIR])
AC_SUBST([RDM_LIBDIR])

#End
AC_OUTPUT
  1. Inside your project directory, run the following command to create the configure script for this host: 
$> cd App
$> touch NEWS README AUTHORS ChangeLog
$> autoreconf -i -f

The "touch" command above will create some empty files required by the autoreconf command

  1. Copy the generated header file (bookStore_structs.h) from the Schema Compile (rdm-compile) step to the project directory.
  2. In your project directory, run the following command which will create the Makefile: 
$> ./configure
  1. Now you can run the command make from the command line to build your executable: make
  2. A bookStore executable should have been created.

This program can now be execute in the same directory where you created the database image in the Create Database (rdm-create) step.

Conclusion

Your program should be fully functional at this point. You set up an Embedded TFS which is used when you are interacting with a database that is not shared with other processes, and you wrote and read rows from the database by interacting with the TFS.

Next, you might want to add some more functionality by deleting a row with rdm_cursorDeleteRow() or update a row with rdm_cursorUpdateRow(). Some other concepts to look over might be:

The full source file can be found here: learn/bookStore_embed.c