Queries Parser

The component Queries Parser allows to context producers retrieve in ease way, information from the Orion ContextBroker.

• Generating a query string
• Retrieving information with a query string

Generating a query string

When you want to generate a query string to retrieve information from the Orion ContextBroker you can use the createQuery() function. This function generates queries in string format, receives as parameter a JSON with the conditions (in form of key-values) of the query and returns the query in string format. The next fragment of code shows an example of this function. The line of code console.log(query) prints the query string in console. Example:

    //Convert JSON to Query string
    let query = ngsi.createQuery({
    "id":"Device.*",
    "type":"Device",
    "options":"keyValues",
    "dateObserved" : ">=2018-02-20T16:54:03.931-06:00"
    })
    console.log(query)

The query can be stored in a variable; in this example, the query generated is stored in the variable query. The following line shows the query converted to string format.

?id=Device.*&Device&type=Device&options=keyValues&q=dateObserved>=2018-02-20T16:54:03.931-06:00

Retrieving information with a query string

The query string generated in the previous the section, can be used with the function getWithQuery() of the ocb-sender module for retrieving information from the ContextBroker. The getWithQuery() function receives as unique parameter the query string. Before using this function, is necessary to import the ocb-sender module in the project, as explained here; also configure the URL for the connection with the Orion ContextBroker instance, function described in this section. The following fragment of code shows an example of the getWithQuery() function, the parameter query makes reference to the query string.

    //Send requests to ContextBroker
    cb.getWithQuery(query)
    .then((result) => console.log(result))
    .catch((err) => console.log(err))