Expression Trees

This is the feature that would allow you to compose a conditional expressions (to filter a data) when doing an operation in the database. This condition can be applied in both push/pull operations (ie: Insert, Delete, Update and Query).

There are 3 ways of composing an expression trees.

Dynamic - it is the most simple and direct way of filterting the results. You can use the dynamic object to filter data.
Linq-Expression - it is the most common way of filtering the data.
Query Objects - it is the most advance, efficient, performant and powerful way of composing the tree expression.

Disclaimer

The support to query objects are massive and well tested with high-quality. However, the Linq-Expression parser of the library is not as extensive as Entity Framework. Therefore, we highly recommend to always use the QueryGroup and QueryField objects when composing a complex expressions.

Dynamic

Below is a sample way of querying via dynamics.

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

Or with multiple column.

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

Please be aware that the compiler does not understand dynamic, any change on the column name would not trigger a pre-compilation exception. Also, the dynamic only supports the expression-equality and cannot be used with other operations (ie: NotEqual, GreaterThan, etc).

Linq-Expression

Below is a sample way of querying via Linq Expression.

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

Or with multiple column.

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

Or with other operations.

using (var connection = new SqlConnection(connectionString).EnsureOpen())
{
    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") });
}

Query Objects

Below is a sample way of querying via QueryField.

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

Or with multiple column.

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

Or with other operations.

using (var connection = new SqlConnection(connectionString).EnsureOpen())
{
    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);
}

Use this way over Linq-Expression if you are composing an advance or complex expression. See the reference implementation here for more details.