DbQuery

DbQuery TypeScript Class Reference

Overview

The DbQuery class provides methods to execute data queries against the local (on-device) database. This is the preferred approach to work with local relational data. It is used to DbQuery to select, insert, update and delete business objects.

There are no properties

Don't instantiate directly instances of the DbQuery class. DbQuery instances are created through a call to the query() method of the BusinessObjectBase assessor. See also BusinessObjectBase.query() method

import {DbQuery} from '@dms';
import { Customer } from '@dms-bo';
...
const query = Customer.query();

▶️ fields(fields: Array<string>): DbQuery<T>

fields method sets the list of the fields to be returned by the executeSelect method of DbQuery. It provides functionality similar to the SELECT clause in a sql statement.

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

//define only 3 fields to be returned
query.fields(['Id','Name','City']);

//method chaining - e.g. calling several method on a single line
query.fields(['Id','Name','City']).filter("Id='123'");

▶️ filter(filterExpression: string): DbQuery<T>

Allows the developer to define a filter to be applied, when using executeSelect() method. The filter expects the same syntax as WHERE clause in sql statement.

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

//equal
query.filter("Id=1123'");

//greater than
query.filter("Revenue > 6000");

//more complex filter with parentess 
query.filter("((Revenue > 6000 or Revenue=0) and (City='Sofia'))");

const result = await query.executeSelect();

//method chaining - e.g. calling several method on a single line
const result2 = await query.fields(['Id','Name','City','Revenue']).filter("City='Dubai'and Revenue>1234").executeSelect();

limit(maxRecords: number): DbQuery<T>

Allows the developer to limit the number of the records returned by the query.

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

//limit to 100 records
query.max(100);
const result = await query.executeSelect();

page(index: number): DbQuery<T>

Allows the developer to define the page number to be returned in page indexing scenarios. This make sense only if the limit() method was used.

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

//limit to 100 records
query.max(100);
//select second page , e.g. records from 100th to 199th
query.page(2);

const result = await query.executeSelect();

group(groupExpression: string): DbQuery<T>

Allows the developer to define a query group expression to be used. This is the same as in the GROUP BY clause in Sql

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

query.group('City, Country');
const result = await query.executeSelect();

//method chaining - e.g. calling several method on a single line
const result2 = await query.group('City, Country').executeSelect();

aggregate(aggregateExpression: string): DbQuery<T>

Allows the developer to define a aggregate expression to be used. This is the same as in aggregates(max, count, min , avg, ...) in Sql Note that the aggregate() method can NOT be used together with fields() method - e.g. the developer must either fields() or aggregate() methods

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

query.aggregate('max(Revenue) as revenue, count(*) as cnt');
const result = await query.executeSelect();

//method chaining - e.g. calling several method on a single line
const result2 = await query.group('City, Country').aggregate('max(Revenue) as revenue, count(*) as cnt').executeSelect();

sort(sortExpression: string): DbQuery<T>

Allows the developer to define a sort expression to be used. This is the same as in ORDER BY clause in Sql

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

query.sort('Revenue asc');
const result = await query.executeSelect();

//method chaining - e.g. calling several method on a single line
const result2 = await query.fields(['City','Country']).sort('Revenue asc').executeSelect();

executeSelect(): Promise<BusinessObjectBase:T>

executeSelect method performs the actual query execution and returns array of objects, which extends class BusinessObjectBase.

import {DbQuery} from '@dms'
import {Customer} from '@dms-bo'

const query = Customer.query();

//fetch all records from the local on-device database
const result = await query.executeSelect();

//iterating over the result set and call the update method for each businessobjectbase instance
//which will execute update operation against the local on-device database 
result.forEach(function(record){
    const customer = (record as Customer);    
    console.log(`Name:${customer.name},Revenue:${customer.Revenue}`);
    customer.Revenue += 1000;
    await customer.update();
});

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