Expression Trees

This feature allows you to compose conditional expressions to filter data during database operations. Conditions can be applied to both push and pull operations (e.g., Insert, Delete, Update, and Query).

Expression trees can be composed using the following objects:

Object	Description
Anonymous Types	The simplest and most direct way to filter results using an anonymous object.
Linq-Expression	The most common way to filter data. Works only with entity-model-based operations.
ExpandoObject or IDictionary<string, object>	The most dynamic way to filter data.
QueryField or QueryGroup	The most advanced, efficient, and powerful way to compose tree expressions, though more verbose.

While the library provides broad support for query objects, the Linq-Expression parser is not as extensive as macro-ORMs. For complex expressions, QueryGroup and QueryField are recommended.

Anonymous Type

Query via an anonymous type:

using (var connection = new SqlConnection(connectionString))
{
    var customer = connection.Query<Customer>(new { Id = 10045 }).FirstOrDefault();
}

Or with multiple columns:

using (var connection = new SqlConnection(connectionString))
{
    var customer = connection.Query<Customer>(new { FirstName = "John", LastName = "Doe" }).FirstOrDefault();
}

The compiler does not validate anonymous types — column name changes do not trigger compile-time exceptions. Additionally, anonymous types only support equality expressions and cannot be used for other comparisons (e.g., not-equal, greater-than, less-than).

Linq-Expression

Query via a Linq expression:

using (var connection = new SqlConnection(connectionString))
{
    var customer = connection.Query<Customer>(e => e.Id == 10045).FirstOrDefault();
}

Or with multiple columns:

using (var connection = new SqlConnection(connectionString))
{
    var customer = connection.Query<Customer>(e => e.FirstName == "John" && e.LastName == "Doe" }).FirstOrDefault();
}

Or with additional operations:

using (var connection = new SqlConnection(connectionString))
{
    var states = new [] { "Chicago", "Washington", "Kansas" };
    var customers = connection.Query<Customer>(e => states.Contains(e.State) && e.IsActive == false && e.DateOfBirth >= DateTime.Parse("1970-01-01") });
}

ExpandoObject and Dictionary<string, object>

Query via an ExpandoObject or IDictionary<string, object>:

using (var connection = new SqlConnection(connectionString))
{
    var where = new Dictionary<string, object>
    {
        { nameof(Customer.Id), 10045 }
    };
    var customer = connection.Query<Customer>(where).FirstOrDefault();
}

Or with multiple columns:

using (var connection = new SqlConnection(connectionString))
{
    var where = new new Dictionary<string, object>
    {
        { nameof(Customer.FirstName), "John") },
        { nameof(Customer.LastName), "Doe" }
    };
    var customer = connection.Query<Customer>(where).FirstOrDefault();
}

Both ExpandoObject and IDictionary<string, object> only support equality expressions and cannot be used for other comparisons (e.g., not-equal, greater-than, less-than).

QueryField/QueryGroup

Query via QueryField:

using (var connection = new SqlConnection(connectionString))
{
    var customer = connection.Query<Customer>(new QueryField(nameof(Customer.Id), 10045)).FirstOrDefault();
}

Or with multiple columns:

using (var connection = new SqlConnection(connectionString))
{
    var where = new []
    {
        new QueryField(nameof(Customer.FirstName), "John"),
        new QueryField(nameof(Customer.LastName), "Doe")
    };
    var customer = connection.Query<Customer>(where).FirstOrDefault();
}

Or with additional operations:

using (var connection = new SqlConnection(connectionString))
{
    var states = new [] { "Chicago", "Washington", "Kansas" };
    var where = new []
    {
        new QueryField(nameof(Customer.State), Operation.In, states),
        new QueryField(nameof(Customer.IsActive),false),
        new QueryField(nameof(Customer.DateOfBirth), Operation.GreaterThanOrEqual, DateTime.Parse("1970-01-01"))
    };
    var customers = connection.Query<Customer>(where);
}

Please visit our Query Expressions reference implementation page for more details.