Retrieve the Columns and Tables of a Database in Postgres - ajax

Question

I am working on a Spring MVC project where I need to get the tables and the attributes of a selected Postgres Database and store them in an array as soon as the page loads.
I have currently written the following ajax call through which am able to retrieve the tables and display under the respective database.
VisualEditor.js
drop: function (e, ui) {
var mouseTop = e.clientY;
var mouseLeft = e.clientX;
var dropElem = ui.draggable.attr('class');
droppedElement = ui.helper.clone();
ui.helper.remove();
$(droppedElement).removeAttr("class");
$(droppedElement).draggable({containment: "container"});
jsPlumb.repaint(ui.helper);
//If the dropped Element is a TABLE then->
if (dropElem == "stream ui-draggable ui-draggable-handle") {
var newAgent = $('<div>');
jsPlumb.addEndpoint(newAgent,connectorProperties);
newAgent.attr('id', i).addClass('streamdrop');
var elemType = "table";
$("#container").addClass("disabledbutton");
$("#toolbox").addClass("disabledbutton");
$('#container').append(newAgent);
$.ajax({
type: "post",
url: "http://localhost:8080/controllers/tables",
cache: false,
success: function(response){
if (response !== "{}"){
var array = response.replace("{", "").replace("}", "");
var index = array.indexOf("[") +1;
var stringval = array.split(":");
var stringval2 = array.substring(index,array.indexOf("]")).split(",");
var db_names = new Array();
var table_names = new Array();
var column_names = new Array();
for(var i = 0 ;i < stringval.length-1 ;i++)
{
db_names[i] = eval(stringval[i]);
if(db_names[i]=="testdb"){
var StreamArray = new Array();
}
var listId = "db"+i;
var dropdownId ="mydrpdown"+i;
table_names[i] = new Array();
$("#lot").append(
"<li onclick='myFunction(\""+dropdownId+"\","+i+","+stringval2.length+")' class='list-group-item dropbtn' id='"+listId+"'> " + db_names[i] +
"</li> "+
"<div id='" + dropdownId +"' class='dropdown-content'> " +
"<a onclick='setDatabase(\""+db_names[i]+"\",\""+listId+"\")'> Make This as Default Database</a>"+
"</div>"
);
$("#databaseID").append(
"<option>" + db_names[i] +"</option>"
);
for(var j=0;j < stringval2.length;j++)
{
/**
* Loading the Predefined Databases and Tables of the Connected DB
*/
var table_id= "tableId"+i+j;
if( eval(stringval2[j]) != null){
table_names[i][j] = eval(stringval2[j]);
if(db_names[i]=="testdb")
{
StreamArray[j] = new Array(4);
StreamArray[j][0] = table_names[i][j];
/**
* table_names array values at the moment are:
* customer,department and students
* So the following ajax call should pass each table name to the listTables
* method in the controller and fetch the respective columns of each table
*/
$.ajax({
type: "post",
url: "http://localhost:8080/controllers/listTables/{tablename}",
data: { tablename: table_names[i][j]} ,
cache: false,
success: function(response){
if (response !== "{}"){
var array = response.replace("{", "").replace("}", "");
var index = array.indexOf("[") +1;
var stringval = array.split(":");
var stringval2 = array.substring(index,array.indexOf("]")).split(",");
var db_names = new Array();
var table_names = new Array();
var column_names = new Array();
for(var i = 0 ;i < stringval.length-1 ;i++){
}
}
}
});
}
$("#lot").append(
"<li class='list-group-item'style = 'display:none' id='"+table_id+"'> "+table_names[i][j]+" </li>");
}
}
$("#lot").append(
"</br>");
array = array.slice(array.indexOf("]") +2);
index = array.indexOf("[") +1;
stringval2 = array.substring(index,array.indexOf("]")).split(",");
}
}
},
error: function(xhr, status, error){
alert("Error while loading the query");
}
});
$("property").show();
$(".toolbox-titlex").show();
$(".panel").show();
I have written 2 ajax calls embedded within to get the table_names in the first go and the column_names following that. But am guessing that this is not a very efficient way. But I am not sure how to get both at the same time.
EditorController.java
#RequestMapping(value= "/tables", method = RequestMethod.POST)
public #ResponseBody
String tables(HttpServletRequest request, HttpServletResponse response)
throws Exception {
Map<String, List<String>> alvalues = new HashMap<String, List<String>>();;
String queryString = request.getParameter("query");
// ApplicationContext context = new ClassPathXmlApplicationContext("Spring-Module.xml");
//CustomerDao customerDAO = (CustomerDao) context.getBean("CustomerDao");
alvalues = customerDAO.getAllTables();
Gson gson = new Gson();
String element = gson.toJson(alvalues);
System.out.println(element);
return element;
}
#RequestMapping(value= "/listTables/{tablename}", method = RequestMethod.POST)
public #ResponseBody
String listTables(HttpServletRequest request, HttpServletResponse response,#PathVariable("tablename") String tablename)
throws Exception {
Map<String, List<String>> alvalues = new HashMap<String, List<String>>();;
String queryString = request.getParameter("query");
alvalues = customerDAO.getAllFields(tablename);
Gson gson = new Gson();
String element = gson.toJson(alvalues);
System.out.println(element);
return element;
}
CustomerDAO.java
public Map<String, List<String>> getAllTables();
public Map<String, List<String>> getAllFields(String tablename);
jdbcCustomerDAO.java
public Map<String, List<String>> getAllTables(){
int k = 1;
Map<String, List<String>> map = new HashMap<String, List<String>>();
ArrayList<String> databases = getAllDatabse();
String sql = "SELECT table_name FROM information_schema.tables WHERE table_schema='public'";
Connection conn = null;
for(int i=0;i<=databases.size();i++)
{
try {
Class.forName("org.postgresql.Driver");
conn = DriverManager.getConnection(
"jdbc:postgresql://localhost:5432/"+databases.get(i),"postgres", "123");
PreparedStatement ps = conn.prepareStatement(sql,ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet rs = ps.executeQuery();
ArrayList<String> alvalues = new ArrayList<String>();
while(rs.next()){
alvalues.add(rs.getString(1));
}
map.put(databases.get(i), alvalues);
rs.beforeFirst();
for (Map.Entry<String, List<String>> entry : map.entrySet()) {
String key = entry.getKey();
List<String> values = entry.getValue();
System.out.println("Key = " + key);
System.out.println("Values = " + values + "n");
}
conn.close();
}
catch(Exception e){
System.out.println(e.getMessage());
}
}
return map;
}
public Map<String, List<String>> getAllFields(String tablename){
int k = 1;
Map<String, List<String>> map = new HashMap<String, List<String>>();
ArrayList<String> databases = getAllDatabse();
String sql = "SELECT column_name FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '"+tablename+"'";
Connection conn = null;
for(int i=0;i<=databases.size();i++)
{
try {
Class.forName("org.postgresql.Driver");
conn = DriverManager.getConnection(
"jdbc:postgresql://localhost:5432/"+databases.get(i),"postgres", "123");
PreparedStatement ps = conn.prepareStatement(sql,ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet rs = ps.executeQuery();
ArrayList<String> alvalues = new ArrayList<String>();
while(rs.next()){
alvalues.add(rs.getString(1));
}
map.put(databases.get(i), alvalues);
rs.beforeFirst();
for (Map.Entry<String, List<String>> entry : map.entrySet()) {
String key = entry.getKey();
List<String> values = entry.getValue();
System.out.println("Key = " + key);
System.out.println("Values = " + values + "n");
}
conn.close();
}
catch(Exception e){
System.out.println(e.getMessage());
}
}
return map;
}
But am not able to get the column names successfully.
Console Log
According to this, the table_names are successfully retrieved but the column names are empty.
INFO : com.postgres.controllers.HomeController - Welcome home! The client locale is en_US.
postgres
postgreside
testdb
Key = postgres
Values = []n
Key = postgreside
Values = [constraints, users, notes, session, projects, databases, tables, columns, index, checksconstraint, additionalproperties, foreignref, primaryref, referenceproperties, department, person]n
Key = postgres
Values = []n
Key = testdb
Values = [customer, department, students]n
Key = postgreside
Values = [constraints, users, notes, session, projects, databases, tables, columns, index, checksconstraint, additionalproperties, foreignref, primaryref, referenceproperties, department, person]n
Key = postgres
Values = []n
Index: 3, Size: 3
{"testdb":["customer","department","students"],"postgreside":["constraints","users","notes","session","projects","databases","tables","columns","index","checksconstraint","additionalproperties","foreignref","primaryref","referenceproperties","department","person"],"postgres":[]}
postgres
postgreside
testdb
postgres
postgreside
testdb
postgres
postgreside
testdb
Key = postgres
Values = []n
Key = postgres
Values = []n
Key = postgres
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Key = testdb
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Index: 3, Size: 3
{"testdb":[],"postgreside":[],"postgres":[]}
Key = testdb
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Index: 3, Size: 3
{"testdb":[],"postgreside":[],"postgres":[]}
Key = testdb
Values = []n
Key = postgreside
Values = []n
Key = postgres
Values = []n
Index: 3, Size: 3
{"testdb":[],"postgreside":[],"postgres":[]}
I would like to have a single method to retrieve the table names and their attributes/columns and store it in the StreamArray so that I don't need to access the DB everytime I need to refer to the related data.
Any suggestions on how I could get the column names and store it in the StreamArray that I've created under the VisualEditor.js will be highly appreciated.

Answer 1

In the general case, you can have more than one database to deal with, more than one schema, and each table name can appear in more than one schema. In your case, there might be more schemas you need to exclude. Or you might decide that only the schema 'public' is relevant. (Be careful with decisions like that.)
select table_catalog, table_schema, table_name, column_name
from information_schema.columns
where table_catalog = 'your_db_name'
and table_schema <> 'information_schema'
and table_schema <> 'pg_catalog'
order by table_catalog, table_schema, table_name, column_name;