Muokkaa

Jaa

Order rows using QueryExpression

  • Artikkeli

To specify the sort order for the rows in tables, use the QueryExpression.Orders or LinkEntity.Orders properties.

Note

The Orders property is read-only. You can set OrderExpression instances to this collection using object initialization or using the QueryExpression.AddOrder method.

LinkEntity doesn't have an AddOrder method. You can use System.Collections.ObjectModel.Collection<T> methods the Orders property inherits.

The default sort order is OrderType.Ascending.

The following query returns account records in ascending order by createdon, name, and accountnumber values.

var query = new QueryExpression(entityName: "account") { 
    ColumnSet = new ColumnSet("name", "accountnumber", "createdon"),
    Orders = {
        { 
            new OrderExpression(
                attributeName: "createdon", 
                orderType: OrderType.Ascending) 
        },
        {
            new OrderExpression(
                attributeName: "name",
                orderType: OrderType.Ascending)
        },
        {
            new OrderExpression(
                attributeName: "accountnumber",
                orderType: OrderType.Ascending)
        },
    }
};

This same query can be composed using the QueryExpression.AddOrder method:

var query = new QueryExpression(entityName: "account") { 
    ColumnSet = new ColumnSet("name", "accountnumber", "createdon")
};
query.AddOrder(attributeName: "createdon", orderType: OrderType.Ascending);
query.AddOrder(attributeName: "name", orderType: OrderType.Ascending);
query.AddOrder(attributeName: "accountnumber", orderType: OrderType.Ascending);

The order of the elements determines how the ordering is applied. To have ordering applied using accountnumber, add that order first:

query.AddOrder(attributeName: "accountnumber", orderType: OrderType.Ascending);
query.AddOrder(attributeName: "createdon", orderType: OrderType.Ascending);
query.AddOrder(attributeName: "name", orderType: OrderType.Ascending);

Descending order

If you want to use descending order, use OrderType.Descending. The following example returns account records with the most recently created records at the top.

var query = new QueryExpression(entityName: "account") { 
    ColumnSet = new ColumnSet("name", "createdon")
};
query.AddOrder(attributeName: "createdon", orderType: OrderType.Descending);

Process LinkEntity orders first

Dataverse always orders columns specified by LinkEntity.Orders after QueryExpression.Orders.

The following example shows a conventional ordering pattern for both LinkEntity and QueryExpression columns.

var query = new QueryExpression(entityName: "account")
{
    ColumnSet = new ColumnSet("name", "accountnumber", "createdon"),
    LinkEntities = {
        new LinkEntity(
            linkFromEntityName:"account",
            linkToEntityName:"account",
            linkFromAttributeName: "parentaccountid",
            linkToAttributeName:"accountid",
            joinOperator: JoinOperator.Inner){
             EntityAlias = "parentaccount",
             Columns = new ColumnSet("name"),
             Orders = {
                {
                    new OrderExpression(
                        attributeName:"name",
                        orderType: OrderType.Ascending)
                }
            }
        }
    },
    Orders = {
                {
                    new OrderExpression(
                        attributeName:"name",
                        orderType: OrderType.Ascending)
                }
    }
};

In this case, the results are ordered using following attributes:

  • First => account.name
  • Last => parentaccountname.name

To ensure the LinkEntity order is applied first, move the OrderExpression from the LinkEntity.Orders to the QueryExpression.Orders above the other OrderExpression, and use the OrderExpression.EntityName to refer to the LinkEntity.EntityAlias value.

var query = new QueryExpression(entityName: "account")
{
    ColumnSet = new ColumnSet("name", "accountnumber", "createdon"),
    LinkEntities = {
        new LinkEntity(
            linkFromEntityName:"account",
            linkToEntityName:"account",
            linkFromAttributeName: "parentaccountid",
            linkToAttributeName:"accountid",
            joinOperator: JoinOperator.Inner){
             EntityAlias = "parentaccount",
             Columns = new ColumnSet("name")
        }
    },
    Orders = {
                {
                    new OrderExpression(
                        attributeName:"name",
                        orderType: OrderType.Ascending){
                        // LinkEntity.EntityAlias value
                        EntityName = "parentaccount"
                    }
                },
                {
                    new OrderExpression(
                        // QueryExpression Columns name
                        attributeName:"name",
                        orderType: OrderType.Ascending)
                }
    }
};

Now, the results are ordered using the following attributes:

  • First => parentaccount.name
  • Last => account.name

Ordering lookup and choice columns

The data contained by most column types is relatively simple and you can perform sorting operations that make sense. Lookup and choice columns are more complex because the data stored in the database isn't meaningful out of context.

Lookup Columns

When you order using lookup columns, the results are sorted using the primary name field for the related table. The database stores a GUID value. The formatted value returned is the corresponding primary name field.

Choice Columns

Choice column values are also sorted using the formatted value rather than the values stored in the database. Data for these columns are stored as integers. The formatted value is a localized label based on the user's language.

Note

Since choice sorting is based on the localized label of the users's language, expect different ordering for the results set if the user's language differs.

Ordering and paging

How a page is ordered makes a big difference when paging data. If the information about how the results are ordered is ambiguous, Dataverse can't consistently or efficiently return paged data.

Specify an order for your query. With FetchXml, if you don't add any order elements to your query, Dataverse adds an order based on the primary key of the table. However QueryExpression does not, and when your query specifies distinct results, no primary key values are returned, so Dataverse can't add this default order. You must specify a paging order. Without any order specified, distinct query results might be returned in random order. OData doesn't provide any option to return distinct results, but you should still apply an order when retrieving paged results.

Paging is dynamic. Each request is evaluated independently as they're received. A paging cookie tells Dataverse the previous page. With this paging cookie data, Dataverse can start with the next record after the last one on the preceding page.

Paging works best going forward. If you go back and retrieve a page you previously retrieved, the results can be different because records could be added, deleted, or modified during since you last retrieved the page. In other words, if your page size is 50 and you go back, you get 50 records, but they might not be the same 50 records. If you keep progressing forward through the pages of a data set, you can expect all the records are returned in a consistent sequence.

Deterministic ordering is important

Deterministic ordering means that there's a way to calculate an order consistently. With a given set of records, the records are always returned in the same order. If you need consistent orders and paging, you must include some unique values or combination of column values that are and specify an order for them to be evaluated.

Nondeterministic example

Let's look at an example that is nondeterministic. This data set contains only State and Status information and is filtered to only return records in an open State. The results are ordered by Status. The first three pages are requested. The results look like this:

State Status Page
Open Active 1 Start
Open Active 1
Open Active 1 End
Open Active
Open Active
Open Inactive
Open Inactive

The paging cookie saves information about the last record on the page. When the next page is requested, the last record from the first page isn't included. However, given the nondeterministic data, there's no guarantee that the other two records on the first page aren't included in the second page.

To achieve deterministic ordering, add orders on columns that contain unique values, or values that are semi-unique.

Deterministic example

This query is like the nondeterministic one, but it includes the Case ID column that includes unique values. It's also ordered by Status, but also ordered using Case ID. The results look like this:

State Status Case ID Page
Open Active Case-0010 1 Start
Open Active Case-0021 1
Open Active Case-0032 1 End
Open Active Case-0034
Open Active Case-0070
Open Inactive Case-0015
Open Inactive Case-0047

In the next page, the cookie will have Case-0032 stored as the last record in the first page, so page two will start with the next record after that record. The results look like this:

State Status Case ID Page
Open Active Case-0010 1 Start
Open Active Case-0021 1
Open Active Case-0032 1 End
Open Active Case-0034 2 Start
Open Active Case-0070 2
Open Inactive Case-0015 2 End
Open Inactive Case-0047

Because this query orders unique column values, the order is consistent.

Best practices for orders when paging data

Note

When possible, queries should order on the primary key for the table because Dataverse is optimized for ordering on the primary key by default. Ordering by non-unique or complex fields cause excess overhead and slower queries.

When you retrieve a limited set of data to display in an application, or if you need to return more than 5,000 rows of data, you need to page the results. The choices you make in determining the order of the results can determine whether the rows in each page of data you retrieve overlaps with other pages. Without proper ordering, the same record can appear in more than one page.

To prevent the same record from appearing in more than one page, apply the following best practices:

It's best to include a column that has a unique identifier. For example:

  • Table primary key columns
  • Autonumber columns
  • User/contact IDs

If you can't include a column with a unique identifier, include multiple fields that will most likely result in unique combinations. For example:

  • First name + last name + email address
  • Full name + email address
  • Email address + company name

Anti-patterns for orders when paging data

The following are ordering choices to avoid:

  • Orders that don't include unique identifiers

  • Orders on calculated fields

  • Orders that have single or multiple fields that aren't likely to provide uniqueness such as:

    • Status and state
    • Choices or Yes/No
    • Name values by themselves. For example name, firstname, lastname
    • Text fields like titles, descriptions, and multi-line text
    • Non unique number fields

Next steps

Learn how to filter rows.

Filter rows