Add query builder struct

src/main/db/query_builder.zig

@@ -16,7 +16,7 @@ fn baseTypeName(comptime T: type) []const u8 {
 }
 
 fn tableName(comptime T: type) String {
-    return util.case.pascalToSnake(baseTypeName(T));
+    return comptime util.case.pascalToSnake(baseTypeName(T));
 }
 
 // Represents a table bound to an identifier in a sql query
@@ -29,6 +29,20 @@ pub const QueryTable = struct {
         const f = @as(std.meta.FieldEnum(self.Model), lit);
         return comptimePrint("{s}.{s}", .{ self.as, @tagName(f) });
     }
+
+    pub fn select(comptime self: QueryTable, comptime lit: @Type(.EnumLiteral)) ResultColumn {
+        return .{
+            .@"type" = std.meta.fieldInfo(self.Model, lit).field_type,
+            .field = self.field(lit),
+        };
+    }
+
+    // returns the declaration to put in the FROM clause
+    fn declarationStr(comptime self: QueryTable) String {
+        comptime {
+            return comptimePrint("{s} AS {s}", .{ tableName(self.Model), self.as });
+        }
+    }
 };
 
 fn makeQueryTable(comptime Model: type, comptime table_index: usize) QueryTable {
@@ -51,6 +65,16 @@ test "QueryTable.field" {
     try std.testing.expectEqualStrings("my_type.id", tbl.field(.id));
 }
 
+test "QueryTable.declarationStr" {
+    const MyTable = struct { id: i64 };
+    const tbl = QueryTable{
+        .Model = MyTable,
+        .as = "some_table",
+    };
+
+    try std.testing.expectEqualStrings("my_table AS some_table", tbl.declarationStr());
+}
+
 test "queryTables constructor" {
     const MyTable = struct { id: i64 };
     const MyOtherTable = struct { val: i64 };
@@ -63,9 +87,14 @@ test "queryTables constructor" {
     try std.testing.expectEqualStrings("my_other_table_1", qt[1].as);
 }
 
-fn map(comptime T: type, comptime R: type, comptime vals: []const T, comptime func: fn (T, usize) R) *const [vals.len]R {
+fn map(comptime T: type, comptime R: type, comptime vals: []const T, comptime func: anytype) *const [vals.len]R {
     var result: [vals.len]R = undefined;
-    for (vals) |v, i| result[i] = func(v, i);
+    if (@typeInfo(@TypeOf(func)).Fn.args.len == 2) {
+        for (vals) |v, i| result[i] = @as(R, func(v, i));
+    } else {
+        for (vals) |v, i| result[i] = @as(R, func(v));
+    }
+
     return &result;
 }
 
@@ -134,3 +163,70 @@ test "Condition.str()" {
         } }).str(),
     );
 }
+
+const ResultColumn = struct {
+    @"type": type,
+    field: []const u8,
+
+    pub fn toSelectClause(comptime self: ResultColumn) String {
+        return self.field;
+    }
+
+    pub fn toStructField(comptime self: ResultColumn) std.builtin.Type.StructField {
+        return .{
+            .name = self.field,
+            .field_type = self.@"type",
+            .default_value = null,
+            .is_comptime = false,
+            .alignment = 0,
+        };
+    }
+};
+
+// Represents a full SQL query
+pub const Query = struct {
+    tables: []const QueryTable,
+    fields: []const ResultColumn,
+    filter: Condition,
+
+    pub fn str(comptime self: Query) String {
+        const table_aliases = map(QueryTable, String, self.tables, QueryTable.declarationStr);
+        const select_clauses = map(ResultColumn, String, self.fields, ResultColumn.toSelectClause);
+        return comptimePrint("SELECT {s} FROM {s} WHERE {s}", .{ join(select_clauses, ", "), join(table_aliases, ", "), self.filter.str() });
+    }
+
+    pub fn rowType(comptime self: Query) type {
+        const struct_fields = map(ResultColumn, std.builtin.Type.StructField, self.fields, ResultColumn.toStructField);
+
+        return @Type(.{ .Struct = .{
+            .layout = .Auto,
+            .fields = struct_fields,
+            .decls = &.{},
+            .is_tuple = true,
+        } });
+    }
+};
+
+test "Query" {
+    const MyTable = struct { id: i64 };
+    const MyOtherTable = struct {
+        val: []const u8,
+    };
+    const qt = queryTables(&.{ MyTable, MyOtherTable, MyTable });
+    const q = comptime Query{
+        .tables = qt,
+        .fields = &.{ qt[0].select(.id), qt[1].select(.val) },
+        .filter = Condition{ .eql = .{ .lhs = qt[0].field(.id), .rhs = qt[2].field(.id) } },
+    };
+
+    try std.testing.expectEqualStrings(
+        "SELECT my_table_0.id, my_other_table_1.val " ++
+            "FROM my_table AS my_table_0, my_other_table AS my_other_table_1, my_table AS my_table_2 " ++
+            "WHERE (my_table_0.id = my_table_2.id)",
+        comptime q.str(),
+    );
+
+    const fields = std.meta.fields(q.rowType());
+    try std.testing.expectEqual(i64, fields[0].field_type);
+    try std.testing.expectEqual([]const u8, fields[1].field_type);
+}