Version 1 (modified by Dominic König, 5 years ago) ( diff )



emDB is a service that provides a database abstraction layer for EdenMobile.



A Table object represents a database table, and can be accessed:

...directly from the emDB service (asynchronously):

emDB.table('tablename').then(function(table) {

...or, where a Resource is available (synchronously):

// Access the table of a Resource
var table = resource.table;

// Access any table via a Resource
var table = resource.getTable('tablename');


To access a Field in the Table, the Table object provides the $ method:

var field = table.$('fieldname');

While it is also possible to access a Field like table.fields['fieldname'], this would not map server-side super-IDs (e.g. pe_id) to the EdenMobile em_object_id. Therefore the $ method is preferrable, especially in cases where the field name is a variable.


With Tables and Fields, it is possible to construct query Expressions, e.g.

var query =;

AND and OR are functions of query expressions:

var query =;

If there are multiple operand expressions in an AND or OR, the global allOf() and anyOf() functions can used to improve readability:

// Multiple operand expressions:
var query =;

// Alternative with anyOf:
var query = anyOf(,,;

Both anyOf and allOf can of course be nested indefinitely.


With a table and a query expression, a Set can be constructed like:

var set = table.where(query);

To extract data from a Set, use select(). This is an asynchronous method, so the result comes in a callback:[field], function(rows) {
    if (rows.len) {
        rows.forEach(function(row) {
            // Do something with the row

The result is an array of Rows.


The Row object implements a $ method again (analogously to accessing fields in a table), but this one accepts both field names and Fields:

// Accessing a column via field name
var value = row.$('fieldname');

// Accessing a column with a Field instance
var value = row.$(table.$('fieldname'));

Using Fields to access column values is recommended (or even necessary) when selecting from joins. Obviously, you can use a local variable for table.$('fieldname') and use that in both the select() and the subsequent column access.


A join can be constructed by calling the join() (=inner join) or left() method of a Table or a Set:


...produces a left join of table with otherTable. The on() method of the Table takes a query expression as argument.

The join() or left() methods always return the Set (if called from a Table, they will create a new Set), so they can be chained both with more .join() resp .left() (to construct a multiple-table join), or .where() to filter the set, and eventually a .select() to extract data.

So it can look like this:

    table.$('name').equals('some string')
    [table.$('name'), otherTable.$('value')], 
    function(rows) {

(written on multiple lines, this becomes very readable - almost undisturbed from the inevitable JS punctuation)

Is is also possible to chain multiple .where()'s, basically producing an AND of all where() expresions in the chain. Surely, where you construct a Set in place, you wouldn't do multiple .where()'s but rather use allOf(). But if you collect filters (e.g. in a loop), you can easily extend the Set by calling .where() multiple times, i.e. instead of:

// Somewhat cumbersome:
for (...) {
    if (query) {
        query = query.and(subQuery);
    } else {
        query = subQuery;
table.where(query).select(...); can do it like:

set = table;
for (...) {
    set = set.where(subQuery);

Orderby and Limitby

The select() method accepts an object with arguments as (optional) second parameter, e.g. limitby and orderby:
    [array of fields], 
        limitby: [0,1], 
        orderby: field
    function(rows) {...}

NB limitby: [0,1] can also be written as simply limitby: 1

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