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Why?

Mascis trys to add a bit more flexibility to how you write your ORM queries. By using references to mapped columns and tables (entity collections) you can write your expressions pretty much how you want.

It Does Not

  • Resolve relationships for you. You can't map OrderItems from Orders and have it auto hydrate that relationship for you. This may come one day but I regard other ORMs implementation of this feature as pretty sucky - mostly because there is no great way to achieve it.

How it works

  • You can build queries by joining tables together, you can either return hydrated entities or return your results as a projection. Each table that is part of the query is represented as an instance of QueryTable<TEntity>. This class has a property, Ex which is of type TEntity. You can refer to this in your linq expressions eg. query.Where(() => table1.Ex.Id == someId). You can also pass around the value of Ex directly. Its a proxy class that the query parser recognises as a reference to a table rather than just a member expression that should resolve to a value. Eg:
var order = query.FromTable.Ex;
query.Where(() => order.Amount > 100m);

Projections

  • Projections build on top of the query system to provide a way to select values into any class (including anonymous classes).

Eg:

var q = mascisSession.Query<Order>();
var projection = q.Project(() => new {
  Amount = q.FromTable.Ex.Amount
});

var results = mascisSession.Execute(projection);

You can also use classes with constructors. Eg:

var q = mascisSession.Query<Order>();
var projection = q.Project(() => new OrderProjection(q.FromTable.Ex.Id, q.FromTable.Ex.Amount) {
  DatePaid = q.FromTable.Ex.DatePaid
  });

var results = mascisSession.Execute(projection);

Aggregates

Yeah don't have support for these yet, first need the ability to group by which will probably be a feature used only in projections.

most of what is below is wrong/changed

Expressions Supported

  • Member expressions e.g. someObject.SomeProperty
  • Member expressions from a table queryTable.Ex.SomeProperty
    • queryTable is an instance of QueryTable. The Ex property is a null reference typed to the entity the query table represents. This is how the expression parser knows what table alias to target and what column to target.
  • Expressions targeting a map. map.GetValue<string>(). map is a mapped expression.

Examples

Creating a proxied instance

var foo = mascisSession.Create<Foo>();

Creating a query

var query = mascisSession.Query<Foo>();

Join a table to query

var table = query.CreateTable<Bar>();
query.FromTable.Join(table, () => query.FromTable.Ex.Id == table.Ex.FooId);

Join a subquery to query

var table = query.CreateTable<Bar>();
var tableFields = {
  fooId = table.Map(()=>table.Ex.FooId);//adding a map causes a table to become a sub query
};
query.FromTable.Join(table, () => query.FromTable.Ex.Id == tableFields.fooId.Value<Guid>());