Custom Connector and Navigation Tables

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JoseCVM wrote:

Is there more in-depth documentation for the Table.View usage (Or for powerquery and connector development in general)? I've read about it, but most of it is very superficial and I'm having trouble understanding what is the state, how do I make my Navigation Table to also be a table view etc.

Also, am I correct in thinking that the OnSelectRows handler will override the behaviour of the "Load" button when I select one of them to load?

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As far as loading goes. It will override that and potentially further operations past the load button. E.g.  you could program it in such that the user loads the table, then filters it, adds a column and does a group by operation to all be folded into a single request to the server, which would ask the server to aggregate the data instead of downloading it all and then aggregating it.

I'm not sure where the definative documentation is for all of this logic. I have access to the source code, so I haven't needed to look for the public documentation on this.

First, make sure you read: https://docs.microsoft.com/en-us/power-query/handlingnavigationtables

You will need to copy the Table.ToNavigationTable to your connector code.

Then you would make a function like this: 

        //listFunction () as {text} -- Produces a list of items the user can select.
        //dataFunction (value as text) as table -- Produces the data for a selected  item
        NavigationTableFromList = (dataFunction as function, listFunction as function, optional isLeaf as logical) as table =>
        let
            _isLeaf = if (isLeaf = null) then true else isLeaf,
            itemKind = if (_isLeaf) then "Table" else "Database",
            View = (state) => Table.View(null, [
                GetType = () => 
                    let
                        tableType = type table [ Name = text, ItemKind = text, Data = table, ItemName = text, IsLeaf = logical ],
                        withKey = Type.AddTableKey(tableType, {"Name"}, true)
                    in
                        withKey meta
                        [
                            NavigationTable.NameColumn = "Name",
                            NavigationTable.DataColumn = "Data",
                            NavigationTable.ItemKindColumn = "ItemKind",
                            Preview.DelayColumn = "ItemName",
                            NavigationTable.IsLeafColumn = "IsLeaf"
                        ],

                GetRows = () => if (state <> null) then state else
                    let
                        list = listFunction(),
                        withName = Table.FromRecords(list, {"Name", "ItemKind", "Parameters"}, MissingField.UseNull),
                        withData = Table.AddColumn(withName, "Data", each dataFunction([Name], [Parameters])),
                        withItemName = Table.AddColumn(withData, "ItemName", each if [Parameters] = null or Record.FieldCount([Parameters]) = 0 then "Table" else null),
                        withoutParameters = Table.RemoveColumns(withItemName, {"Parameters"}),
                        withIsLeaf = Table.AddColumn(withoutParameters, "IsLeaf", each isLeaf),
                        navTable = Table.ToNavigationTable(withIsLeaf, {"Name"}, "Name", "Data", "ItemKind", "ItemName", "IsLeaf")
                    in
                        navTable,

                OnSelectRows = (selector) =>
                    let
                        condition = RowExpression.From(selector),
                        kind = condition[Kind],
                        leftKind = condition[Left][Kind],
                        member = condition[Left][MemberName],
                        value = condition[Right][Value]
                    in
                        if (kind = "Binary" and leftKind = "FieldAccess" and member = "Name") then
                            Table.FromRecords({[
                                Name = value,
                                Data = dataFunction(value),
                                ItemKind = "Table"
                                ItemName = value,
                                IsLeaf = true
                            ]})
                        else
                            ...
            ])
        in
            View(null),