[tablemodelview] Fixing JSON api/read serializable issue

[john-bodley]

This PR resolves an issue with tablemodelview/api/read which throws the following exception,

TypeError: Object of type Database is not JSON serializable

i.e., it's trying to to serialize the Database object to JSON which is defined as one of the FAB list_columns. The remedy is to simply reference the Database.name attribute as opposed to the Database object.

Attached is a screenshot, note I've kept the label unchanged so the UI remains unchanged:

and here's the corresponding API response (truncated):

{
  "count": 11, 
  "label_columns": {
    "cache_timeout": "Cache Timeout", 
    "changed_by": "Changed By", 
    "changed_by_": "Changed By", 
    "changed_by_fk": "Changed By Fk", 
    "changed_on": "Changed On", 
    "changed_on_": "Last Changed", 
    "columns": "Columns", 
    "created_by": "Created By", 
    "created_by_fk": "Created By Fk", 
    "created_on": "Created On", 
    "database": "Database", 
    "database_id": "Database Id", 
    "database_name": "Database", 
    "default_endpoint": "Default Endpoint", 
    "description": "Description", 
    "fetch_values_predicate": "Fetch Values Predicate", 
    "filter_select_enabled": "Enable Filter Select", 
    "id": "Id", 
    "is_featured": "Is Featured", 
    "is_sqllab_view": "SQL Lab View", 
    "link": "Table", 
    "main_dttm_col": "Main Datetime Column", 
    "metrics": "Metrics", 
    "modified": "Modified", 
    "offset": "Offset", 
    "owner": "Owner", 
    "params": "Params", 
    "perm": "Perm", 
    "schema": "Schema", 
    "slices": "Associated Charts", 
    "sql": "Sql", 
    "table_name": "Table Name", 
    "template_params": "Template parameters", 
    "user_id": "User Id"
  }, 
  "list_columns": [
    "link", 
    "database_name", 
    "changed_by_", 
    "modified"
  ], 
  "modelview_name": "TableModelView", 
  "order_columns": [
    "modified"
  ], 
  "page": null, 
  "page_size": null, 
  "pks": [
    1, 
    2, 
    3, 
    4, 
    5, 
    6, 
    7, 
    8, 
    9, 
    10, 
    11
  ], 
  "result": [
    {
      "changed_by_": "", 
      "database_name": "main", 
      "link": "<a target=\"_blank\" href=\"/superset/explore/table/1/\">energy_usage</a>", 
      "modified": "an hour ago"
    }, 
   ...

to: @michellethomas @mistercrunch
cc: @graceguo-supercat @timifasubaa

[pierrelafortune]

this is awesome thank you!!! 🚀

[codecov-io]

Codecov Report

Merging #6023 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6023      +/-   ##
==========================================
+ Coverage   77.73%   77.85%   +0.11%     
==========================================
  Files          46       46              
  Lines        9398     9400       +2     
==========================================
+ Hits         7306     7318      +12     
+ Misses       2092     2082      -10

Impacted Files	Coverage Δ
superset/connectors/sqla/views.py	64.34% <ø> (ø)	⬆️
superset/connectors/sqla/models.py	81.2% <100%> (+0.82%)	⬆️
superset/db_engine_specs.py	55.7% <0%> (+0.87%)	⬆️

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