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Using Pre-defined JSON Templates

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Demonstrates how to predefine a JSON template, and then use it to emit JSON with variable substitutions.

Note: This example requires Chilkat v9.5.0.67 or greater.

Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // One way to create JSON is to do it in a straightforward manner:
    const json = try chilkat.JsonObject.init();
    defer json.deinit();
    json.setEmitCompact(false);
    json.updateString("id", "0001") catch {};
    json.updateString("type", "donut") catch {};
    json.updateString("name", "Cake") catch {};
    json.updateString("image.url", "images/0001.jpg") catch {};
    json.updateInt("image.width", 200) catch {};
    json.updateInt("image.height", 200) catch {};
    json.updateString("thumbnail.url", "images/thumbnails/0001.jpg") catch {};
    json.updateInt("thumbnail.width", 32) catch {};
    json.updateInt("thumbnail.height", 32) catch {};
    std.debug.print("{s}\n", .{try json.emit(alloc)});

    // The JSON created by the above code:

    //     {
    //       "id": "0001",
    //       "type": "donut",
    //       "name": "Cake",
    //       "image": {
    //         "url": "images/0001.jpg",
    //         "width": 200,
    //         "height": 200
    //       },
    //       "thumbnail": {
    //         "url": "images/thumbnails/0001.jpg",
    //         "width": 32,
    //         "height": 32
    //       }
    //     }

    // An alternative is to predefine a template, and then use it to emit with variable substitutions.
    // For example:

    const json_template = try chilkat.JsonObject.init();
    defer json_template.deinit();
    json_template.updateString("id", "{$id}") catch {};
    json_template.updateString("type", "donut") catch {};
    json_template.updateString("name", "{$name}") catch {};
    json_template.updateString("image.url", "{$imageUrl}") catch {};
    // The "i." indicates that it's an integer variable.
    json_template.updateString("image.width", "{$i.imageWidth}") catch {};
    json_template.updateString("image.height", "{$i.imageHeight}") catch {};
    json_template.updateString("thumbnail.url", "{$thumbUrl}") catch {};
    json_template.updateString("thumbnail.width", "{$i.thumbWidth}") catch {};
    json_template.updateString("thumbnail.height", "{$i.thumbHeight}") catch {};
    // Give this template a name.
    json_template.predefine("donut") catch {};

    // --------------------------------------------------------------------------
    // OK, the template is defined.  Defining a template can be done once
    // at the start of your program, and you can discard the jsonTemplate object (it
    // doesn't need to stick around..)

    // Now we can create instances of the JSON object by name:
    const json_donut = try chilkat.JsonObject.init();
    defer json_donut.deinit();
    json_donut.setEmitCompact(false);
    json_donut.loadPredefined("donut") catch {};
    std.debug.print("{s}\n", .{try json_donut.emit(alloc)});

    // The output is this:

    //     {
    //       "id": "{$id}",
    //       "type": "donut",
    //       "name": "{$name}",
    //       "image": {
    //         "url": "{$imageUrl}",
    //         "width": "{$i.imageWidth}",
    //         "height": "{$i.imageHeight}"
    //       },
    //       "thumbnail": {
    //         "url": "{$thumbUrl}",
    //         "width": "{$i.thumbWidth}",
    //         "height": "{$i.thumbHeight}"
    //       }
    //     }

    // Finally, we can substitute variables like this:
    const donut_values = try chilkat.Hashtable.init();
    defer donut_values.deinit();
    donut_values.addStr("id", "0001") catch {};
    donut_values.addStr("name", "Cake") catch {};
    donut_values.addStr("imageUrl", "images/0001.jpg") catch {};
    donut_values.addInt("imageWidth", 200) catch {};
    donut_values.addInt("imageHeight", 200) catch {};
    donut_values.addStr("thumbUrl", "images/thumbnails/0001.jpg") catch {};
    donut_values.addInt("thumbWidth", 32) catch {};
    donut_values.addInt("thumbHeight", 32) catch {};

    // Emit with variable substitutions:
    const omit_empty = true;
    std.debug.print("{s}\n", .{try json_donut.emitWithSubs(alloc, donut_values, omit_empty)});

    // Output:

    //     {
    //       "id": "0001",
    //       "type": "donut",
    //       "name": "Cake",
    //       "image": {
    //         "url": "images/0001.jpg",
    //         "width": 200,
    //         "height": 200
    //       },
    //       "thumbnail": {
    //         "url": "images/thumbnails/0001.jpg",
    //         "width": 32,
    //         "height": 32
    //       }
    //     }

    // Change some of the values:
    donut_values.addStr("id", "0002") catch {};
    donut_values.addStr("imageUrl", "images/0002.jpg") catch {};
    donut_values.addStr("thumbUrl", "images/thumbnails/0002.jpg") catch {};

    std.debug.print("{s}\n", .{try json_donut.emitWithSubs(alloc, donut_values, omit_empty)});

    // Output:

    //     {
    //       "id": "0002",
    //       "type": "donut",
    //       "name": "Cake",
    //       "image": {
    //         "url": "images/0002.jpg",
    //         "width": 200,
    //         "height": 200
    //       },
    //       "thumbnail": {
    //         "url": "images/thumbnails/0002.jpg",
    //         "width": 32,
    //         "height": 32
    //       }
    //     }
}