Is it possible get the model from a string?

Question

I'm trying to build a dynamic filter, where the user can search for columns in tables. To that I'm trying to use System.Linq.Dynamic.Core

var data = Db.MyTable1.Select($"new ({string.Join(", ", queryParams.Columns)})", "T", StringComparison.OrdinalIgnoreCase);

But now I also would like to get the table from the parameter string, something like

var query = Db.Get(queryParams.Table);
query = query.Select...

Working with EntityFrameworkCore 3.1, is there a way to achieve this?

score 0 · Accepted Answer · answered Apr 25 '20 at 05:01

You can override the Query method of DbContext.

First,create a custom Query method:

  public static partial class CustomExtensions
    {
        public static IQueryable Query(this DbContext context, string entityName) =>
            context.Query(context.Model.FindEntityType(entityName).ClrType);

        static readonly MethodInfo SetMethod = typeof(DbContext).GetMethod(nameof(DbContext.Set));

        public static IQueryable Query(this DbContext context, Type entityType) =>
            (IQueryable)SetMethod.MakeGenericMethod(entityType).Invoke(context, null);
    }

Then, you need to store the table names and types of all the tables involved in the Dictionary.

 Dictionary<string, Type> TableTypeDictionary = new Dictionary<string, Type>()
    {
          { "Teachers", typeof(Teachers) },//store the tables name and type.
          { "Students", typeof(Students) },
          { "Product", typeof(Product) }
          //...
    };

Last, use db to call Query method :

  var query = Db.Query(TableTypeDictionary[queryParams.Table]).Select($"new ({string.Join(",", queryParams.Columns)})", "T", StringComparison.OrdinalIgnoreCase);

You can also bring "Namespace.MyTable" in the Query method. At this time, you need to rewrite the Query method to another writing method, please refer to this.

Is it possible get the model from a string?

1 Answers1