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Filtering in Query objects

  • 项目

You specify filters in a query to restrict the data in the resulting dataset. A filter applies conditions on fields in a table that is associated with the query. For a record to be included in the resulting dataset, its values in these fields must meet the conditions of the filter.

Filtering overview

There are different ways to filter on fields of a query. You can set up filters on a field directly in the query object or use the AL filter methods that are outlined in the following table.

Filter Description
Filter directly on a data item in query object You can set the DataItemTableFilter property of a data item to filter on a field in the table of the data item. You can apply the filter to any field in the table, not just fields that are defined as columns in the resulting dataset. A data item filter can't be overwritten from AL code.

See Filtering on data items in a query object.
Filter directly on a column in a query object You can set the ColumnFilter property of a column control to filter on the source field of the column. A filter on a column is overwritten by the SetFilter and SetRange methods from AL code.

See Filtering on columns and filter rows in query object.
Add a filter row to a query object A filter row lets you add a filter on a field that won't be included in the resulting dataset, but can be changed from AL code. To set up a row filter add a filter control referencing the field that you want to filter, and then set its ColumnFilter Property. A filter row is like a data item filter except a filter on a filter row is overwritten by the SetFilter and SetRange methods from AL code.

See Filtering on columns and filter rows in query object.
Use SetFilter or SetRange method calls You can call the SetFilter method method from AL code to set a filter on a field that is exposed through a column or filter row. The filter that is set by the SetFilter method overwrites any filter that is applied to a column or filter row on the same field by the ColumnFilter Property.

You can call the SetRange method method from AL code to set a filter on a field that is exposed through a column or filter row. The filter that is set by the SetRange method overwrites any filter that is applied to column or filter row on the same field.

See Filtering using SetFilter and SetRange methods.

Filtering on data items in a Query object

To specify filters on a data item, you set the DataItemTableFilter property of a data item. DataItemTableFilter property has the following syntax:

DataItemTableFilter = String;

where String is the filter expression.

You can apply a filter on any field in a table, not just those fields that are represented by a column in the query object.

A data item filter is static, which means that it can't be overwritten by the ColumnFilter Property, filter controls or by the SetFilter or SetRange methods in AL code. If one of these filter types is applied to the same field as the data item filter, then the filters are combined. In logical terms, this combination corresponds to an "AND" operation. For example, if the data item filter applies a filter on a field to include values greater than 10 (>10) and a column filter applies a filter on the same field to include values less than 50 (<50), then the resultant filter includes values that are greater than 10 and less than 50 (10< value <50).

The DataItemTableFilter Property corresponds to a WHERE clause in an SQL SELECT statement. For more information, see Equivalent SQL SELECT Statements for Query Filters.

Example

The following query object links table 18 Customer and table 37 Sales Line to get the number of line items in each sales for customers. The DataItemTableFilter property is used to only include rows in which the number of line items is greater than 10.

query 50100 "Customer_Sales_Quantity"
{
    QueryType = Normal;

    elements
    {
        dataitem(C; Customer)
        {
            column(Customer_Number; "No.")
            {
            }

            column(Customer_Name; Name)
            {
            }

            dataitem(SL; "Sales Line")
            {
                DataItemLink = "Sell-to Customer No." = c."No.";
                SqlJoinType = InnerJoin;
                DataItemTableFilter = Quantity = filter(> 10);

                column(Qty; Quantity)
                {
                }
            }
        }
    }
}

Filtering on columns and filter rows in query object

Unlike data item filters, filters on a column or filter row are dynamic and can be overwritten from AL code at runtime by a call to the SetFilter or SetRange method, if the method sets a filter on the same field.

You use filters on a column to filter on fields that are included in the dataset. To apply a filter on a column, you set the ColumnFilter Property of the column. You can apply a filter on any column, including aggregated columns that are applied an aggregate method by the Method Property. The ColumnFilter property has the following syntax:

ColumnFilter = String;

where String is the filter expression.

Adding a filter row

Use a filter row when you want to filter the query on a field, but you don't want to include the field in the dataset. For example, you might want to filter a date field on a specific date, but you don't want to include the date in the dataset. To set up a filter row, first add a filter element that specifies the table field on which you want to filter, Then, add the ColumnFilter property to set the conditions of the filter.

Example

The following query object links the Customer table and the Sales Line table and retrieves the total quantity of line items ordered for each customer. The query includes the following filters.

  • A filter on the Qty column to include only records from the Sales Line table where the total quantity is less than 50.

  • A filter on filter row for the Location Code field of the Sales Line table that includes only records where the location code is WHITE.

query 50100 "Customer_Sales_Quantity"
{
    QueryType = Normal;

    elements
    {
        dataitem(C; Customer)
        {
            column(Customer_Number; "No.")
            {
            }

            column(Customer_Name; Name)
            {
            }

            dataitem(SL; "Sales Line")
            {
                DataItemLink = "Sell-to Customer No." = c."No.";
                SqlJoinType = InnerJoin;
                DataItemTableFilter = Quantity = filter(> 10);

                column(Qty; Quantity)
                {
                    Method = Sum;
                    ColumnFilter = Qty = filter(< 50);
                }

                filter(Location_Code; "Location Code")
                {
                    ColumnFilter = Location_Code = const('White');
                }
            }
        }
    }
}

In an SQL SELECT statement, filters on a column or filter row that don't apply an aggregate method, as with the Location_Code filter row in the example, would correspond to a WHERE clause. Filters on a columns or filter rows that do apply a totals method, as with the Quantity column in the example, would correspond to a HAVING clause. For more information, see Equivalent SQL SELECT Statements for Query Filters.

Filtering using SetFilter and SetRange methods

AL code includes the SetFilter and SetRange methods that you can use to apply a filter on a field that is represented as a column or filter row in a query. The SetFilter and SetRange methods enable you to set filters programmatically on a query at runtime. You use the SetRange method to filter on a range of values in a column or filter row. The SetFilter method is more versatile than the SetRange method and enables you to filter a field based on a filter expression.

These methods overwrite any filter on the same field that is set on a column or filter row by the ColumnFilter property. If a SetFilter or SetRange method filters on the same field as a filter on a data item, as specified by the DataItemTableFilter Property, then the method filter and DataItemTableFilter property filter are combined.

Calling the SetFilter and SetRange methods

You can call the SetFilter and SetRange method from the AL code of the Business Central object that runs the query object or from the OnBeforeOpen Trigger of the query object.

To call the SetFilter method, you use the following code.

Query.SetFilter(Column, String)

To call the SetRange method, you use the following code.

Query.SetRange(Column, FromValue, ToValue)

where:

  • Query is a variable of the Query type that specifies the query object.

  • Column is the name of the column or filter row as defined by its Name property.

  • String is the filter expression.

  • FromValue is the lower value of the range.

  • ToValue is the higher value of the range.

For more information about these methods and important behavior, see SetFilter method and SetRange method (Query).

Example

Referring to the query example in the previous sections, you can add the following code to the OnBeforeOpen trigger of the query object to change the filters on the Quantity column and the Location\_Code filter row to include quantities of in the range of 10 to 50 and a location code of RED.

trigger OnBeforeOpen()
begin
    currQuery.SetRange(Qty, 10, 50);
    currQuery.SetFilter(Location_Code, '=RED');
end;

Equivalent SQL SELECT Statements for Query Filters

If you're familiar with SQL, then it's helpful to know how filtering in Business Central queries relates to SQL statements. To specify filters in an SQL statement, you use WHERE and HAVING clauses. The WHERE clause filters on fields. The HAVING clause filters on the results that have aggregated values as applied by of a totals method.

The following example shows the corresponding SQL SELECT statement for the previous data item filter example that links the Customer and Sales Line tables and filters on the Quantity field.

SELECT Customer."No.", Customer.Name, "Sales Line".Quantity  
FROM Customer LEFT OUTER JOIN "Sales Line"  
ON Customer."No." = "Sales Line".Sell-to Customer No.  
WHERE "Sales Line"."Quantity" > 10

The following example shows the corresponding SQL SELECT statement for the previous column and filter row example that links the Customer and Sales Line tables and filters on the Location Code field and the total sum of the Quantity field.

SELECT Customer."No.", Customer.Name, SUM("Sales Line".Quantity) as Qty  
FROM Customer LEFT OUTER JOIN "Sales Line"  
  ON Customer."No." = "Sales Line".Sell-to Customer No.  
WHERE "Sales Line"."Location Code" = WHITE  
GROUP BY Customer."No."  
HAVING Qty  50

Query object
Aggregating data
SetFilter method
SetRange method