Crestron CT-3000 Especificações descarregar pdf (Página 39)

Crestron e-control Database Manager SW-DBM

39 •• The Database File Installation & Reference Guide — DOC. 5823

In general, successive queries work like this: Recall that picking an item from a

touchscreen scroller sends a Pick signal to the server which normally sends a series

of Data signals in response, containing field values from the associated record in the

database table. (See “Picking a Record” on page 40 for more information on scroller

picks.)

However, in a successive query with v levels, the first v-1 levels, called successive

levels, behave differently. Picking a record from a successive level causes the server

to respond by advancing to the next query level. Only the final pick, on the v

query,

displays the picked record as usual.

Each successive level of query always results in a “narrower” recordset, a subset of

the previous query. However, it is important to note that while the number of records

represented in succeeding levels is always less than (or equal to) the number of

records represented in the preceding levels, the number of records actually displayed

in a succeeding level may be more. This is because these queries are always

DISTINCT type queries — wherein duplicates are eliminated. Another example

makes this clear:

Suppose the database table contains entries for 100 reps distributed among only

five different countries. Since this is a DISTINCT query, only the five distinct

values appear in the level 1 (“country”) query. Had this been a regular (non-

DISTINCT) query, all 100 records would have appeared.

The fields used to display each level are listed on separate lines in the list fields

column of the Queries table. Each line may contain a single field (as would be

the case in the example above), or a list of fields (separated by commas) for a multi-

column list display.

Queries table showing the query used for demo2.

Demo 2, Successive Query, uses the successive query signals to let the user “drill

down” from a general list of music genres to a specific artist, album, and track. At

the start of the application, the scroller displays the list of genres available (for

example, Rock and Reggae). Once the user has selected a genre, the scroller displays

a list of artists who have albums of that genre. Next the user can select an album, and

the tracks for the album are displayed. When the user selects a track, the track is

played.

Displaying a Successive Query

A single scroller signal block is used to display all the levels in a successive query.

(The single-scroller approach was chosen to keep the number of signals within

reason. A separate scroller for each level of a five- or six-level query could end up

using hundreds of signals.) The server displays movement between levels by

refreshing the scroller with a new list of items to choose from, and by sending a

GoLevelEcho

signal (if defined).

This scroller may be represented in either of two ways on the touchscreen:

1. As a single structure on a single touchscreen page

2. The structure may be reproduced on a series of pages, one page for each level.

The following standard scroller signals get special treatment during a successive

query:

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 ... 93 94

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