ServiceStack服务请求设计

Question

I am keen on using ServiceStack and have created a little test app with a simple customer service:

  [Route("/customers/{id}")]
    public class GetCustomer : IReturn<Customer>
    {
        public int Id { get; set; }
    }
    [Route("/customers/search")]
    public class FindCustomers : IReturn<List<Customer>>
    {
        public string LastName { get; set; }
        public int Age { get; set; }
        public string? City { get; set; }
    }

    public class CustomerService : IService
    {
        public object Get(GetCustomer request)
        {
            var db = new WebServDb();
            var customer = db.FirstOrDefault<Customer>("WHERE Id=@0", request.Id);
            return customer;
        }
        public object Get(FindCustomers request)
        {
            var db = new WebServDb();
            var customers = new List<Customer>();
            if (request.City.HasValue)
                customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2", request.LastName, request.Age, request.City);
            else
                customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1", request.LastName, request.Age);
            return customers;
        }
    }

The FindCustomers request DTO contains 3 properties that can be used to search for customers. Based on which properties are set I need to query the DB differently. So what is the best way to do this? For example, if I add another property such as:

 [Route("/customers/search")]
    public class FindCustomers : IReturn<List<Customer>>
    {
        public string LastName { get; set; }
        public int Age { get; set; }
        public string? City { get; set; }
        public string? ZipCode { get; set; }
    }

to the FindCustomers DTO, I would also have to change the service Get method to:

public object Get(FindCustomers request)
{
    var db = new WebServDb();
    var customers = new List<Customer>();
    if (request.City.HasValue && request.ZipCode.HasValue)
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2 AND ZipCode=@3", request.LastName, request.Age, request.City, request.ZipCode);
    else if (request.City.HasValue)
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2", request.LastName, request.Age, request.City);
    else
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1", request.LastName, request.Age);
    return customers;
  }

So for each property I add/remove from the request DTO I need to modify my Get method. Is there better way do this? A more generic way to check for properties set and querying the DB?

Would it be better to have specific request DTOs such as FindCustomersByLastNameCity , FindCustomersByLastNameZipCode , etc. as well as corresponding specific Get methods in the CustomerService ?

Answer 1

Would it be better to have specific request DTOs such as FindCustomersByLastNameCity, FindCustomersByLastNameZipCode
I would avoid this if possible as it goes against the 'Message Based Services' benefits/approach encouraged by ServiceStack.

Is there better way do this?
I don't know if I have a 'better way' but below are two options I have tried. The second option is still a 'work in progress' and is meant to be more 'abstract' but I modified it to work with your example and to hopefully inspire other ideas.

Option 1 using ExpressionVisitor:

public object Get(FindCustomers request)
{
    var customers = new List<Customer>();

    var ev = OrmLiteConfig.DialectProvider.ExpressionVisitor<Customer>();
    ev.Where(c => c.LastName == request.LastName).And(c => c.Age == request.Age);
    AddOptionalFilters(ev, request);

    customers = Db.Select<Customer>(ev);

    return customers;
}

private void AddOptionalFilters(SqlExpressionVisitor<Customer> expressionVisitor, FindCustomers request)
{
    if (request.City.HasValue)
    { expressionVisitor.Where(c => c.City == request.City); }

    if (request.ZipCode.HasValue)
    { expressionVisitor.Where(c => c.ZipCode == request.ZipCode); }
} 

Option 2 using the SqlBuilder from Dapper:

public object Get(FindCustomers request)
{
    var customers = new List<Customer>();          

    var sqlAndParams = SqlAndParameters("SELECT * From Customers", request); //this returns a tuple of the sql string and the parameters
    customers = Db.Query<Customer>(sqlAndParams.Item1, sqlAndParams.Item2);

    return customers;
}

public virtual Tuple<String, IDictionary<string, object>> SqlAndParameters(string sql, FindCustomers request)
{
    var builder = new SqlBuilder();
    var selector = builder.AddTemplate(sql);
    var sqlParams = new ExpandoObject() as IDictionary<string, object>;

    builder.Where("LastName=@LastName");
    sqlParams.Add("LastName", request.LastName);

    builder.Where("Age=@Age");
    sqlParams.Add("Age", request.Age);

    if (request.City.HasValue)
    {
        builder.Where("City=@City");
        sqlParams.Add("City", request.City);
    }

    if (request.ZipCode.HasValue)
    {
        builder.Where("ZipCode=@ZipCode");
        sqlParams.Add("ZipCode", request.ZipCode);
    }

    return Tuple.Create(selector.RawSql, sqlParams);
}