What is entity reference and Query Expression ? Please give some simple examples

Question

What is EntityReference and QueryExpression? Please give me some simple examples.

Answer 1

EntityReference

It is used for lookup fields in 365 – e.g. to link records via a 1 to many relationship. The lookup field is shown on the ‘child’. You need to specify the ‘parent’ entity type and record id.

For example if you are creating a accountand want to set the primary contact.

Entity account = new Entity("account"); 
account["name"] = "James Account"; 
account["primarycontactid"] = new EntityReference("contact", contactId);
service.Create(account);

QueryExpression

QueryExpression provides an object model to construct a query. Queries can also be created using FetchXML, a proprietary XML based query language.

For example of you wanted to retrieve all contacts full name and telephone number.

QueryExpression query = new QueryExpression()
{
    Distinct = false,
    EntityName = Contact.EntityLogicalName,
    ColumnSet = new ColumnSet("fullname", "address1_telephone1"),
};
DataCollection<Entity> entityCollection = _service.RetrieveMultiple(query).Entities;