Provided data source did not match an array, Observable, or DataSource at getTableUnknownDataSourceError

Question

I am new to Angular and Angular Material ,

Without Angular Materail it is working fine

<table>
  <tr>
    <th>City</th>  
    <th>State</th>
  </tr>

  <tr>
      <td>{{ varEmp?.address.city}}</td>
      <td>{{ varEmp?.address.state}}</td>

    </tr>

</table>

With Angular Material it is not Working

<table mat-table [dataSource]="varEmp" class="mat-elevation-z8">


  <!-- Position Column -->
  <ng-container matColumnDef="city">
    <th mat-header-cell *matHeaderCellDef> City</th>
    <td mat-cell *matCellDef="let element"> {{element?.address.city}} </td>
  </ng-container>

  <!-- Name Column -->
  <ng-container matColumnDef="state">
    <th mat-header-cell *matHeaderCellDef> State</th>
    <td mat-cell *matCellDef="let element"> {{element?.address.state}} </td>
  </ng-container>

<tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
  <tr mat-row *matRowDef="let row; columns: displayedColumns;"></tr>
</table>

In component I declared variable

displayedColumns: string[] = ['city','state'];

briefy described component code to reduce complexity

Json Object

{"address":
   {"city": "Karwar", "state": "Karnataka"}
}

Answer 1

I stumbled upon this issue as I had a static data source of json format and I needed to dump it in a mat-table.

The most common reason for this behavior is poor format of json data. The json data expected by mat-table should be in the format [{...}, {...}, {...}]. If you cannot change the format of the json data, simply convert the data to Array like this

var dataArr = new Array(jsonData));

and it would work.

Note - Converting it to array would add an extra layer of square brackets to the data. You might need to change the [dataSource] property in mat-table to dataArr[0].

<table mat-table [dataSource]="dataArr[0]">