Power Query Expression error: A value of type "Record" cannot converted into type "Text"

Question

I have the issue that I'm not able to execute the following code. The syntax seems to be okay, but when I try to execute it, I get the response, that:

Expression.Error: We cannot convert a value of type Record to type "Text". Details: Value=[Record] Type=[Type]

let
    body="{
    ""page"": ""1"",
    ""pageSize"": ""100"",
    ""requestParams"": {
        ""deviceUids"": [
            ""xxx-yyy-xxx-yyyy-xxxx"",
            ""yyy-xxx-yyy-xxxx-yyyy"",
            ""aaa-bbb-aaa-bbbb-aaaa"",
            ""ccc-ddd-ccc-dddd-cccc""
        ],
        ""entityColumns"": [
            {
                ""entityId"": ""144"",
                ""joinColumnName"": ""device_uid"",
                ""columnName"": ""device_random_date""
            }
        ],
        ""columnNames"": [
            ""ts"",
            ""device_uid"",
            ""1"",
            ""32"",
            ""55"",
            ""203"",
            ""204""
        ],
        ""startUnixTsMs"": ""1583413637000"",
        ""endUnixTsMs"": ""1583413640000"",
        ""columnFilters"": [
            {
                ""filterType"": ""eq"",
                ""columnName"": ""55"",
                ""value"": ""1234""
            }
        ],
        ""sortOrder"": [
            {
                ""column"": ""ts"",
                ""order"": ""DESC""
            },
            {
                ""column"": ""55"",
                ""order"": ""ASC""
            }
        ],
        ""entityFilters"": [
            {
                ""entityId"": ""144"",
                ""entityEntryIds"": [
                    ""12345-221-232-1231-123456""
                ]
            }
        ]
    }
    }",
    Parsed_JSON = Json.Document(body),
    BuildQueryString = Uri.BuildQueryString(Parsed_JSON),
    Quelle = Json.Document(Web.Contents("http://localhost:8101/device-data-reader-api/read-paginated/xxx-xxx-yyyy-yyyy", [Headers=[#"Content-Type"="application/json"], Content = Text.ToBinary(BuildQueryString)]))
in
    Quelle

I tried to remove the quotes of the numbers, but this leads to the same issue, as system complains it cannot convert numbers into text. I need the body which needs to be handed over with the request in order to do a POST request. What I'm doing wrong?

Answer 1

Since you seem to want to send this as application/json, I think you would change this bit in your code:

Content = Text.ToBinary(BuildQueryString)

to:

Content = Text.ToBinary(body)

and then you'd also get rid of the lines below (since you don't need them):

Parsed_JSON = Json.Document(body),
BuildQueryString = Uri.BuildQueryString(Parsed_JSON),

I don't think you would need Uri.BuildQueryString unless you wanted to send as application/x-www-form-urlencoded (i.e. URL encoded key-value pairs).

---

Unrelated: If it helps, you can build the structure in M and then use JSON.FromValue to turn the structure into bytes which can be put directly into the POST body. Untested example is below.

let
    body = [
        page = "1",
        pageSize = "100",
        requestParams = [
            deviceUids = {
                "xxx-yyy-xxx-yyyy-xxxx",
                "yyy-xxx-yyy-xxxx-yyyy",
                "aaa-bbb-aaa-bbbb-aaaa",
                "ccc-ddd-ccc-dddd-cccc"
            },
            entityColumns = {
                [
                    entityId = "144",
                    joinColumnName = "device_uid",
                    columnName = "device_random_date"
                ]
            },
            columnNames = {
                "ts",
                "device_uid",
                "1",
                "32",
                "55",
                "203",
                "204"
            },
            startUnixTsMs = "1583413637000",
            endUnixTsMs = "1583413640000",
            columnFilters = {
                [
                    filterType = "eq",
                    columnName = "55",
                    value = "1234"
                ]
            },
            sortOrder = {
                [
                    column = "ts",
                    order = "DESC"
                ],
                [
                    column = "55",
                    order = "ASC"
                ]
            },
            entityFilters = {
                [
                    entityId = "144",
                    entityEntryIds = {
                        "12345-221-232-1231-123456"
                    }
                ]
            }
        ]
    ],
    Quelle = Json.Document(
        Web.Contents(
            "http://localhost:8101/device-data-reader-api/read-paginated/xxx-xxx-yyyy-yyyy",
            [
                Headers = [#"Content-Type" = "application/json"],
                Content = Json.FromValue(body)
            ]
        )
    )
in
    Quelle

It might look a little weird (since M uses [] instead of {}, {} instead of [] and = instead of :), but just mentioning in case it helps.