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Get the Report →Write a Simple Go Application to work with Harvest Data on Linux
Use CData ODBC drivers and unixODBC to create a simple Go app with live connectivity to Harvest data.
Go is an open source programming language that enables you to easily build software on Linux/UNIX machines. When Go is paired with the ODBC Driver for Harvest and unixODBC you are able write applications with connectivity to live Harvest data. This article will walk you through the process of installing the ODBC Driver for Harvest, configuring a connection using the unixODBC Driver Manager, and creating a simple Go application to work with Harvest data.
Using the CData ODBC Drivers on a Unix/Linux Machine
The CData ODBC Drivers are supported in various Red Hat-based and Debian-based systems, including Ubuntu, Debian, RHEL, CentOS, and Fedora. There are also several libraries and packages that are required, many of which may be installed by default, depending on your system. For more information on the supported versions of Linux operating systems and the required libraries, please refer to the "Getting Started" section in help documentation (installed and found online).
Installing the Driver Manager
Before installing the driver, you need to be sure that your system has a driver manager. For this article, you will use unixODBC, a free and open source ODBC driver manager that is widely supported.
For Debian-based systems like Ubuntu, you can install unixODBC with the APT package manager:
apt-get install unixodbc unixodbc-dev
For systems based on Red Hat Linux, you can install unixODBC with yum or dnf:
yum install unixODBC unixODBC-devel
The unixODBC driver manager reads information about drivers from an odbcinst.ini file and about data sources from an odbc.ini file. You can determine the location of the configuration files on your system by entering the following command into a terminal:
odbcinst -j
NOTE: You may need to install odbcinst. Use the following command in a terminal:
apt install odbcinst
The output of the command will display the locations of the configuration files for ODBC data sources and registered ODBC drivers. User data sources can only be accessed by the user account whose home folder the odbc.ini is located in. System data sources can be accessed by all users. Below is an example of the output of this command:
DRIVERS............: /etc/odbcinst.ini
SYSTEM DATA SOURCES: /etc/odbc.ini
FILE DATA SOURCES..: /etc/ODBCDataSources
USER DATA SOURCES..: /home/myuser/.odbc.ini
SQLULEN Size.......: 8
SQLLEN Size........: 8
SQLSETPOSIROW Size.: 8
Installing the Driver
You can download the driver in standard package formats: the Debian .deb package format or the .rpm file format. Once you have downloaded the file, you can install the driver from the terminal.
The driver installer registers the driver with unixODBC and creates a system DSN, which can be used later in any tools or applications that support ODBC connectivity.
For Debian-based systems like Ubuntu, run the following command with sudo or as root:
dpkg -i /path/to/package.deb
For systems that support .rpms, run the following command with sudo or as root:
rpm -i /path/to/package.rpm
Once the driver is installed, you can list the registered drivers and defined data sources using the unixODBC driver manager:
List the Registered Driver(s)
odbcinst -q -d
CData API Driver for ODBC
...
List the Defined Data Source(s)
odbcinst -q -s
CData API Source
...
To use the CData API Driver for ODBC with unixODBC, you need to ensure that the driver is configured to use UTF-16. To do so, edit the INI file for the driver (cdata.odbc.api.ini), which can be found in the lib folder in the installation location (typically /opt/cdata/cdata-odbc-driver-for-api), as follows:
cdata.odbc.api.ini
...
[Driver]
DriverManagerEncoding = UTF-16
Modifying the DSN
When the driver is installed, a system DSN should be predefined. You can modify the DSN by editing the system data sources file (/etc/odbc.ini) and defining the required connection properties. Additionally, you can create user-specific DSNs that will not require root access to modify in $HOME/.odbc.ini.
Start by setting the Profile connection property to the location of the Harvest Profile on disk (e.g. C:\profiles\Harvest.apip). Next, set the ProfileSettings connection property to the connection string for Harvest (see below).
Harvest API Profile Settings
To authenticate to Harvest, you can use either Token authentication or the OAuth standard. Use Basic authentication to connect to your own data. Use OAuth to allow other users to connect to their data.
Using Token Authentication
To use Token Authentication, set the APIKey to your Harvest Personal Access Token in the ProfileSettings connection property. In addition to APIKey, set your AccountId in ProfileSettings to connect.
Using OAuth Authentication
First, register an OAuth2 application with Harvest. The application can be created from the "Developers" section of Harvest ID.
After setting the following connection properties, you are ready to connect:
- ProfileSettings: Set your AccountId in ProfileSettings.
- AuthScheme: Set this to OAuth.
- OAuthClientId: Set this to the client ID that you specified in your app settings.
- OAuthClientSecret: Set this to the client secret that you specified in your app settings.
- CallbackURL: Set this to the Redirect URI that you specified in your app settings.
- InitiateOAuth: Set this to GETANDREFRESH. You can use InitiateOAuth to manage how the driver obtains and refreshes the OAuthAccessToken.
/etc/odbc.ini or $HOME/.odbc.ini
[CData API Source]
Driver = /opt/cdata/cdata-api-driver-for-api/lib/libapiodbc.x64.so
Description = My Description
Profile = C:\profiles\Harvest.apip
ProfileSettings = 'APIKey = my_personal_key
AccountId = _your_account_id'
For specific information on using these configuration files, please refer to the help documentation (installed and found online).
Creating a Simple Go App for Harvest Data
With the Driver Manager installed and the DSN configured, you are ready to create a simple Go application to work with your Harvest data. To start, install a Go driver for ODBC databases. While there are several options available, this article will use the odbc driver found at https://github.com/alexbrainman/odbc.
Installing ODBC on Linux
There are a series of steps required to install the ODBC driver for Go.
- Create the $HOME/golang/go path (if it does not exist) by entering the following commands in a terminal:
mkdir /root/golang mkdir /root/golang/go
- Define the GOPATH environment variable:
export GOPATH=$HOME/golang/go
-
Create a module inside the new Go directory:
cd $GOPATH go mod init myproject
- Install the Go driver for ODBC databases:
go get http://github.com/alexbrainman/odbc
Now you are ready to create and execute a simple Go application.
Sample Go Application
The sample application issues a simple SQL SELECT query for Harvest data and displays the results. Create the directory $GOPATH/src/cdata-odbc-harvest and create a new Go source file, copying the source code from below.
cdata-odbc-harvest.go
package main
import (
_ "github.com/alexbrainman/odbc"
"database/sql"
"log"
"fmt"
)
func main() {
db, err := sql.Open("odbc",
"DSN=CData API Source")
if err != nil {
log.Fatal(err)
}
var (
id string
clientname string
)
rows, err := db.Query("SELECT Id, ClientName FROM Invoices WHERE State = ?", "open")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
for rows.Next() {
err := rows.Scan(&id, &clientname)
if err != nil {
log.Fatal(err)
}
fmt.Println(id, clientname)
}
err = rows.Err()
if err != nil {
log.Fatal(err)
}
defer db.Close()
}
In the terminal, navigate to the Go application directory and build the application:
go build
After the application builds, you will be able to execute the application, displaying your Harvest data:
./cdata-odbc-harvest
At this point, you have a simple Go application for working with Harvest data. From here, you can easily expand the application, adding deeper read functionality through familiar SQL queries.