How can I pass a list of objects through an url to an ASP.NET Web API to query a database table?

Question

I need to basically pass a list of objects each has 3 parameters variable name, operator, and value.

I have tried using

public async Task<ActionResult> GetAPIData([FromQuery] Condition[] conditions) 

where condition is

public class Condition
{
    public string variable { get; set; }
    public string op { get; set; }
    public double value { get; set; }
}

but I just can't get it to pass the items across every time I call the API "conditions" is empty.

It's a messy URL but swagger gives me

http://localhost:5001/api/datatable?conditions=%7B%0A%20%20%22variable%22%3A%20%22vara%22%2C%0A%20%20%22op%22%3A%20%22%3E%22%2C%0A%20%20%22value%22%3A%2020%0A%7D&conditions=%7B%0A%20%20%22variable%22%3A%20%22varb%22%2C%0A%20%20%22op%22%3A%20%22%3E%22%2C%0A%20%20%22value%22%3A%2010%0A%7D

var t = conditions.Length;
IQueryable<ScreenerData> query = _context.datatable;

foreach (var condition in conditions)
{
    string variable = condition.variable;
    string _operator = condition.op;
    double value = condition.value;

    switch (_operator)
    {
        case "==":
            query = query.Where(data => data.GetType().GetProperty(variable).GetValue(data, null).Equals(value));
            break;

        case "!=":
            query = query.Where(data => !data.GetType().GetProperty(variable).GetValue(data, null).Equals(value));
            break;

        case ">":
            query = query.Where(data => Convert.ToDouble(data.GetType().GetProperty(variable).GetValue(data, null)) > value);
            break;

        case "<":
            query = query.Where(data => Convert.ToDouble(data.GetType().GetProperty(variable).GetValue(data, null)) < value);
            break;

        // Handle other operators as needed

        default:
            // Handle unsupported operators or throw an exception
            return BadRequest("Unsupported operator");
    }
}

var filteredData = await query.Where(data => data.Data != null)
                  .Select(data => data.Id)
                  .ToListAsync();

filteredData basically returns the entire dataset because conditions is empty and thus no filtering based on the operator is happening.

Answer 1

First I suggest you to not send this data as fromquery, but if you want to do with it here is the code to pass the array in fromquery from C#.

{
    new Condition {
      Variable = "Variable1",
      Op = ">",
      Value = 10.5
    },
    new Condition {
      Variable = "Variable2",
      Op = "<",
      Value = 20.0
    }
    // Add more conditions as needed
};

var apiUrl = "http://localhost:5001/api/datatable";

var queryString = string.Join("&", conditions.Select(c =>
    $"conditions=
     {Uri.EscapeDataString(c.Variable)}: 
     {Uri.EscapeDataString(c.Op)}
     {c.Value}")
);

var fullUrl = $"{apiUrl}?{queryString}";```

And from PostMan you can call this API as:
http://localhost:5001/api/datatable?conditions=Variable1:>:10.5&conditions=Variable2:<:20.0

Answer 2

It seems that Swagger is currently unable to produce a correct query string for these cases. The correct query string is of the form ?conditions[0].variable=variable1&conditions[0].op=someOperator&conditions[0].value=10.5&conditions[1]... and you keep adding the same pattern, increasing the index counter for every condition.

So as you have seen, the query string name conditions is not very pretty. I suggest you change your action signature to:

public async Task<ActionResult> GetAPIData([FromQuery(Name = "cnd")] Condition[] conditions)

This way, instead of using conditions[], you would use cnd[], which is shorter and singular.