On the indexeddb i want to look if there is a key permanent and do some actions. But if not, i want to make some other actions. I can do the actions if the permanent is there, however when it is not I can get the onerror to work. Is the onerror suppose to do this thing? How can I check if there is not value in it?
var hashtype = 'permanent';
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function() {
var ivrame = getPermanent.result.value;
};
getPermanent.onerror = function() {
console.log('onerror')
};
See the note under https://w3c.github.io/IndexedDB/#dom-idbobjectstore-get - the get method yields success with undefined if there is no matching record.
So you have a few options:
Use get(key) and test the result for undefined. This works unless undefined is a value you expect to store (it's a valid value)
Use count(key) - the result will be 1 if present, 0 if absent. Easy if you're just testing for existence, but doesn't get you the record.
Use openCursor(key) and test to see if the request's result is a cursor (record present as request.result.value) or undefined (no record in range)
For your code:
var hashtype='permanent';
// #1: Use get
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function() {
if (getPermanent.result === undefined) {
// no record with that key
} else {
var value = getPermanent.result;
}
};
// #2: Use count
var getPermanent = store.count(hashtype);
getPermanent.onsuccess = function() {
if (getPermanent.result === 0) {
// no record with that key
} else {
...
}
};
// #3: Use cursor
var getPermanent = store.openCursor(hashtype);
getPermanent.onsuccess = function() {
var cursor = getPermanent.result;
if (!cursor) {
// no record with that key
} else {
var value = cursor.value;
}
};
The function assigned to request.onsuccess is a callback function that is always called, regardless of whether the value is present in the store. When there is no corresponding object in the store, the result object will be undefined. When there is a corresponding object in the store, the result object will be defined. So you simply need to check if the object is defined from within the onsuccess callback function.
request.onerror is a separate callback from request.onsuccess. onerror gets called when there is some type of failure in indexedDB (e.g. something like you tried to get a value from a store that doesn't exist, or you tried to put a duplicate object into a store that doesn't permit duplicates). request.onerror does not get called when no value is found as a result of calling store.get, because that is not considered an 'error' in the failure sense.
So, what you want to do is something like this:
var hashtype='permanent';
var getPermanent = store.get(hashtype);
getPermanent.onsuccess = function(event) {
//var ivrame=getPermanent.result.value;
var result = getPermanent.result;
if(result) {
console.log('Got a result!', result);
var ivrame = result;
} else {
console.log('Result was undefined! No matching object found');
}
};
getPermanent.onerror = function() {
console.log('Something went wrong trying to perform the get request');
};
Do not try and access request.result.value. There is no such thing in the case of a get request. When using store.get, request.result contains the matching object you want, or is undefined. When using store.openCursor, request.result contains the cursor, which is defined if there is at least one matching object and you have not already iterated past it. To get the matching object at the cursor's current position, you would use cursor.value. Here, cursor.value will always be defined, because cursor would otherwise be undefined, and you would obviously check for that beforehand.
Instead of using getPermanent.result to access data provided by 'get' request it is better to use event.target.result. It also can be compared with undefined to check absence of requested key:
db = this.result;
var tr = db.transaction("data");
var objstore = tr.objectStore("data");
var getres = objstore.get(0);
getres.onsuccess = function(event)
{
if(event.target.result.data === undefined)
console.log("key not found");
}
Related
I am not able to retrieve properties when looping through objects stored in indexedDB. When i attempt to get objects trough tasksStore.get(i);, i get the error Cannot read property 'property' of undefined at IDBRequest.getTasks.onsuccess, however, if I change it to tasksStore.get(1);, it works fine, and gets object with id=1 x index's length.
I've tried checking the typeof of both ways, and they both return number.
//success handler on connection
request.onsuccess = function(e) {
db = request.result;
//define store index
tasksStore = tasksTx.objectStore("tasksStore");
//error handler on result of the request
db.onerror = function(e) {
console.log("ERROR " + e.target.errorCode);
}
//variable for counting objects in the index
let amountOfTasks = tasksIndex.count();
//error handler
amountOfTasks.onerror = function() {
console.log("There was an error finding the amount of tasks")
}
//success handler
amountOfTasks.onsuccess = function() {
for (var i = 1; i < amountOfTasks.result; i++) {
let getTasks = tasksStore.get(i);
let getTasksElementContainer = document.getElementById("list-tasks");
let createTasksList = document.createElement("li");
createTasksList.id = "task-" + i;
getTasks.onerror = function() {
console.log("There was an error looping through the tasks")
}
getTasks.onsuccess = function() {
console.log(getTasks.result.title); //getTasks.result works, getTasks.result.title does not.
getTasksElementContainer.appendChild(createTasksList);
//JSON stringify to return object in string format, and not [Object object]
createTasksList.innerHTML = JSON.stringify(getTasks.result.title);
}
}
}
}
When you call IDBObjectStore.get with a key that doesn't exist in your database, the resulting value is undefined. That likely explains why sometimes getTasks.result is undefined.
If you're still having trouble, you'd likely be well served by making a self-contained reproducible example. You'll probably find your own bug in the process of doing that. If not, it's easier to get more specific help on Stack Overflow if you have some code that other people can run to directly observe the problem (so including database creation and inserting data).
Again, i got some question on indexeddb. I´m getting a
InvalidStateError: A Mutation operation was attempted on a database
that did not allow mutations.
and also an
AbortError
Here is my code:
DB_LINK.prototype.pushStoreNumeric = function ()
{
// Saving Values
var _temp = 0;
var _version = this.link.version;
var _name = this.link.name;
var that = this;
var _objectStoreNames = this.link.objectStoreNames;
// Close DB
this.link.close();
this.state = 4;
// Reopen Database
this.req = indexedDB.open(_name,_version+1); // Abort error here
this.req.onupgradeneeded = function () {
that.state = 1;
// Get Number of object stores
_temp = _objectStoreNames.length;
if(_temp != 0)
{
// Already object stores: read highest value
_temp = parseInt(_objectStoreNames[_objectStoreNames.length - 1]);
}
that.link.createObjectStore(_temp); // InvalidStateError here
};
I have marked per comment where the errors occur.
The InvalidStateError occures first, the AbortError follows.
I am calling this function inside another onsuccess function of the same database. Might this be the problem?
What is this.link? That's probably the problem. You need to be doing createObjectStore on the database instance created by the indexedDB.open request. So either this.req.result.createObjectStore or (if you change to this.req.onupgradeneeded = function (e) {) you could use e.target.result.createObjectStore.
More generally, I can't really comment on what your code is supposed to be doing because I can only see a snippet, but it looks really weird how you are incrementing the version every time this is called. Probably you don't actually want to be doing that. You might want to read a bit more documentation.
I'm hoping someone can help with what is likely a simple answer - but I'm ready to bash my head against the wall....again.
I have a function which makes a JSON call to an API, and then pushes the results into an array. The function appears to work just fine as my console.log is showing that the array is populated correctly.
I'm struggling with how to access the values of the modified twichResult object (after the function has run), so that I can do 'stuff' with it. e.g. display the value of the 'status' property onscreen etc... I give some examples of what I've tried in the in the large commented out section.
I'd really appreciate some intelligence weighing in on this as I've exhausted my resources. Thanks in advance.
<script type="text/javascript">
$(document).ready(function() {
var twitchResult = {results:[]};
var channel = { logo:"", display_name:"", status:"", url:"" };
var finalUrl = "https://api.twitch.tv/kraken/streams/freecodecamp?callback=?"
getTwitchers (finalUrl, "freecodecamp");
console.log(twitchResult);
// How do I access the individual values in the object TwitchResult?
// I get "undefined" in the console if I try to access the object's property values
// I've tried every way I can think of to get 'into' the returned object :
// console.log(twitchResult.results);
// console.log(twitchResult["results"])
// console.log(twitchResult.results.status)
// console.log(twitchResult[0])
// console.log(twitchResult[0][0])
// etc etc
function getTwitchers (url, item) {
$.getJSON(url, function(data) {
var obj = data.stream;
// Check if the object is not valid using (obj == null) which is shorthand for both null and undefined
if (obj == null) {
if (obj === undefined) {
channel.display_name = item;
channel.status = "closed";
console.log ("this is undefined");
}
else {
channel.display_name = item;
channel.status = "offline";
console.log("this is null");
}
}
else {
channel.logo = obj.channel.logo;
channel.display_name = obj.channel.display_name;
channel.status = obj.channel.status;
channel.url = obj.channel.url;
console.log("valid entry");
}
twitchResult["results"].push(channel);
// twitchResult.results.push(channel);
// console.log(twitchResult);
});
}
});
</script>
$.getJSON is making an ajax-request. You must handle this request from within the request handler. When getTwichers returns, twichResults is not yet set.
There are methods to delay Program execution, until twichResults is done, but You should not think of using them, since they would delay program execution. The idea of ajax is to execute things asynchronously, without disturbing the rest of the execution flow. If the code You want to execute depends on the json, then You should add it to the handle in $.getJSON. Just write a new function (e.g. continue_execution(twichResult)) and invoke it right after twitchResult["results"].push(channel);. Just don't do anything after getTwitchers(...).
By the way: It is a good habit to define functions, before they are used, because it follows the flow the human eye reads the code and there are programming languages, which depend on this style of declaring function.
If this is unclear to You, then add a comment.
I'm running a script on an apache webserver on a linux box. Based on the parameter I want to change the name of variable(or set it)
The idea is that humDev(lines 11 and 14) is named humDev21 for example. Where devId is the number 21 in this example.
My script looks like this:
function getHumDev(devId){
$.ajax({
async: false,
url: "/url" + devId,
success: function(result) {
var array = result["Device_Num_" + devId].states;
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
humDev = array[i].value;
}
}
return humDev;
};
objectFindByKey(array, 'service', 'some');
}
});
};
If Im looking in the wrong direction, please do let me know. Maybe its bad practice what Im trying. The reason I want to have the object a unique name is because this function is called several times by another function, based on the content of an array. But when I have the humDev object named without the number suffix to make it unique, the content of the object is getting mixed up between the different calls.
I may be off base but I am making some assumptions based on what I understand of what you are trying to do.
First, you need to understand how to do file I/O in node.js. So lets start there:
var pathToFile, //set with file path string
fs = require('fs'), //require the file i/o module API
bunchOfHumDevs = {},
fileContents; //we'll cache those here for repeated use
fs.readFile(pathToFile, function(err, result) {
if (err) {
throw new Error(); //or however you want to handle errors
} else {
fileContents = JSON.parse(result); //assumes data stored as JSON
}
});
function getHumDev(devId) {
//first make sure we have fileContents, if not try again in 500ms
if (!fileContents) {
setTimeout(function() {
getHumDev(devId);
}, 500);
} else {
var array = fileContents["Device_Num_" + devId].states,
i = array.length,
//if 'service' and 'some' are variable, make them params of
//getHumDev()
while (i--) {
if (array[i]['service'] === 'some') {
//store uniquely named humDev entry
bunchOfHumDevs['humDev' + devId.toString()] = array[i].value;
break; //exit loop once a match is found
}
}
}
return null;
}
getHumDev(21);
assuming a match is found for the devId 21, bunchOfHumdevs will now have a property 'humDev21' that is the object (value?) in question. Also, the fileContents are now cached in the program so you don't have to reopen it every time you call the function.
I'm trying to take the values of a certain key from an indexed DB and add them to an array, this array works fine within the onsuccess function but is empty after it. I'm guessing by the order the two years[0] that are logged to the console appear that problem is something to do with being asynchronous. I'm obviously not really understanding what order things are happening in and how to achieve what I want. Could someone please help me understand what the problem is and maybe point me in the right direction to overcoming it.
// the array I want the values in
var years = new Array();
// function retrieves all objects between certain years, low and high
function getYears(low, high){
var request = window.indexedDB.open("matchDB", 1);
request.onerror = function(event) {console.log("onerror");}
request.onsuccess = function(event) {
var db = event.target.result;
var objectStore = db.transaction(["matches"], 'readonly').objectStore("matches");
var index = objectStore.index("year");
var range = IDBKeyRange.bound(low, high, true, true);
var request = index.openCursor(range);
request.onsuccess = function(evt) {
var cursor = evt.target.result;
if (cursor) {
var matchList = cursor.value;
// the value of the key year is pushed into the array years
years.push(matchList.year);
console.log(years[0]); // this works
cursor.continue();
}
}
console.log(years[0]); //this is undefined
}
}
request.onsuccess is a callback function that will get called when the asynchronous request has completed. Notice that you are just assigning a function to the onsuccess property, you are not executing the function. It could be executed seconds later.
The code following it will continue to be executed after it has been defined, so console.log(years[0]) will be called immediately after which is why it prints out "undefined" since the callback method hasn't been executed yet. All of your code that deals with "years" should go inside the callback.
If you don't want to shove all of your code inside the callback, just define another method and call it from within the callback method.
function handleRequest(evt) {
var cursor = evt.target.result;
if (cursor) {
var matchList = cursor.value;
// the value of the key year is pushed into the array years
years.push(matchList.year);
console.log(years[0]); // this works
cursor.continue();
}
}
var request = index.openCursor(range);
request.onsuccess = function(evt) {
handleRequest(evt);
}
}