How to serialize the query results into JSON?

[huaxk]

An error occurred when serializing the query results into JSON：

lib/std/json/stringify.zig:673:25: error: Unable to stringify type 'type'
                else => @compileError("Unable to stringify type '" ++ @typeName(T) ++ "'"),

zig version is 0.14.0-dev.3062, the code is as follows:

const std = @import("std");
const jq = @import("jetquery");
const Schema = @import("Schema.zig");  // same as jetquery porject

const Repo = jq.Repo(.postgresql, Schema);

pub fn Query(comptime model: anytype) type {
    return jq.Query(.postgresql, Schema, model);
}

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer std.debug.assert(gpa.deinit() == .ok);
    const allocator = gpa.allocator();

    var repo = try Repo.loadConfig(
        allocator,
        .development,
        .{},
    );
    defer repo.deinit();

    const human = try Query(.Human).first(&repo);
    defer repo.free(human);

    const json = try std.json.stringifyAlloc(allocator, human, .{});
    defer allocator.free(json);
    std.debug.print("{s}", .{json});
}

The type of 'human' returned from query is: ?jetquery.Query.Statement(...).QueryResultType(), it should be an optional struct because QueryResultType() build a struct using the schema 'Human' model's fields.

@(typeInfo(@TypeOf(human)) return: @as(builtin.Type, .{ .optional = .{ .child = jetquery.Query.Statement(...).QueryResultType() } })

I don't know why it can't match the branche of '.optional' during the json serialization process.

[huaxk]

I can declare the query return type:

    const Hm = @TypeOf(Query(.Human).select(.{ .id, .name })).ResultType;

quivalent to the following struct that is dynamically generated during the compilation phase：

    const Hm = struct {
        id: i32,
        name: []const u8,
        __jetquery: struct {
            original_values: struct {
                id: i32,
                name: []const u8,
            },
        },
    };

and then serialize to json:

    const h = Hm{
        .id = 2,
        .name = "hello",
        .__jetquery = .{ .original_values = .{ .id = 0, .name = "" } },
    };
    const json = try std.json.stringifyAlloc(allocator, h, .{});
    defer allocator.free(json);
    std.debug.print("{s}\n", .{json});

still encountering error:

lib/std/json/stringify.zig:673:25: error: Unable to stringify type 'type'
                else => @compileError("Unable to stringify type '" ++ @typeName(T) ++ "'"),

but if i use the directly declared struct above, it can run normally.
Is there anything wrong with my code?

[bobf]

@huaxk See this code:

https://github.com/jetzig-framework/jetquery/blob/main/src%2Fjetquery%2FQuery.zig#L1303

JetQuery stores two comptime fields on each ResultType whose values are of type type which (I think) is causing the std json serializer to choke.

Zmpl filters out values like this before serializing.

Unfortunately I can't implement toJson as a member function of ResultType as Zig deliberately prohibits this, but it could be implemented as a utility function in JetQuery (to transform the value into a JSON-friendly type or to serialize directly).

With a bit of meta programming you should be able to implement something ad hoc for now, but feel free to make a PR if you see a nice way to solve this. I'll give it some thought in the meantime.