Eduard Eduard - 1 month ago 6
C# Question

Creating dynamic queries with entity framework

I would like to know what is the best way of creating dynamic queries with entity framework and linq.

I want to create a service that has many parameters for sorting and filtering (over 50). I will be getting object from gui where these will be filled out... and query will be executed from a single service method.

I looked around And I saw that I could dynamically create a string that can be executed at the end of my method. I don't like this way very much. Is there a better way to do this? Preferably type safe with compile check?

Answer

You could compose an IQueryable<T> step by step. Assuming you have a FilterDefinition class which describes how the user wants to filter ...

public class FilterDefinition
{
    public bool FilterByName { get; set; }
    public string NameFrom { get; set; }
    public string NameTo { get; set; }

    public bool FilterByQuantity { get; set; }
    public double QuantityFrom { get; set; }
    public double QuantityTo { get; set; }
}

... then you could build a query like so:

public IQueryable<SomeEntity> GetQuery(FilterDefinition filter)
{
    IQueryable<SomeEntity> query = context.Set<SomeEntity>();
    // assuming that you return all records when nothing is specified in the filter

    if (filter.FilterByName)
        query = query.Where(t => 
            t.Name >= filter.NameFrom && t.Name <= filter.NameTo);

    if (filter.FilterByQuantity)
        query = query.Where(t => 
            t.Quantity >= filter.QuantityFrom && t.Quantity <= filter.QuantityTo);

    return query;
}
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