在Azure Table Storage SDK中，GenerateFilterCondition的用途是什么？

Question

In the Azure Table Storage SDK documentation , there are numerous examples of constructing LINQ queries over Tables using code in the form:

TableQuery<CustomerEntity> query = new TableQuery<CustomerEntity>().Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "Smith"));

I understand that GenerateFilterCondition creates a predicate to pass to Where - which works in the same way a (for example) Func<CustomerEntity, bool> would, but I can't find anything that explains why it's required as opposed to writing:

TableQuery<CustomerEntity> query = new TableQuery<CustomerEntity>().Where(c => c.PartitionKey == "Smith");

What does this helper method do for you that writing a straightforward lambda expression like 'normal' LINQ does not?

Answer 1

May be it caused by strong assumption, that you will almost always query data by specifing RowKey and PartitionKey - it is fast(due to inner azure storage tables architecture) and predictable, but if you want to build more complex search condition, you should use TableQuery.GenerateFilterCondition builder instead of standart Entity Framework .Where like predicate, ie Expression<Func<T, bool>> . Also I think TableQuery.GenerateFilterCondition will not offer you something special except of goal opportunities.

If you want to use comfortable predicate syntax, you can use Azure.TableStorage.API library, which allow you to write queries like this:

var api = new AzureTableStorageAPI();
var date = new DateTime(1990, 1, 10);
var persons = api.GetEntities<Person>(x => x.BirthDay > date && x.PartitionKey == "Man" && (x.Age > 30 || x.Name == "Mike"));