Index.Primary property (DAO)

Applies to: Access 2013, Office 2013

Sets or returns a value that indicates whether an Index object represents a primary key index for a table (Microsoft Access workspaces only).

Syntax

expression .Primary

expression A variable that represents an Index object.

Remarks

The Primary property setting is read/write for a new Index object not yet appended to a collection and read-only for an existing Index object in an Indexes collection. If the Index object is appended to the TableDef object but the TableDef object isn't appended to the TableDefs collection, the Index property is read/write.

A primary key index consists of one or more fields that uniquely identify all records in a table in a predefined order. Because the index field must be unique, the Unique property of the Index object is set to True. If the primary key index consists of more than one field, each field can contain duplicate values, but each combination of values from all the indexed fields must be unique. A primary key index consists of a key for the table and usually contains the same fields as the primary key.

Note

You don't have to create indexes for tables, but in large, unindexed tables, accessing a specific record can take a long time. The Attributes property of each Field object in the Index object determines the order of records and consequently determines the access techniques to use for that index. When you create a new table in your database, it's a good idea to create an index on one or more fields that uniquely identify each record, and then set the Primary property of the Index object to True.

When you set a primary key for a table, the primary key is automatically defined as the primary key index for the table.

Example

This example uses the Primary property to designate a new Index in a new TableDef as the primary Index for that table. Note that setting the Primary property to True automatically sets Unique and Required properties to True as well.

    Sub PrimaryX() 
     
     Dim dbsNorthwind As Database 
     Dim tdfNew As TableDef 
     Dim idxNew As Index 
     Dim idxLoop As Index 
     Dim fldLoop As Field 
     Dim prpLoop As Property 
     
     Set dbsNorthwind = OpenDatabase("Northwind.mdb") 
     
     ' Create and append a new TableDef object to the 
     ' TableDefs collection of the Northwind database. 
     Set tdfNew = dbsNorthwind.CreateTableDef("NewTable") 
     tdfNew.Fields.Append tdfNew.CreateField("NumField", _ 
     dbLong, 20) 
     tdfNew.Fields.Append tdfNew.CreateField("TextField", _ 
     dbText, 20) 
     dbsNorthwind.TableDefs.Append tdfNew 
     
     With tdfNew 
     ' Create and append a new Index object to the 
     ' Indexes collection of the new TableDef object. 
     Set idxNew = .CreateIndex("NumIndex") 
     idxNew.Fields.Append idxNew.CreateField("NumField") 
     idxNew.Primary = True 
     .Indexes.Append idxNew 
     Set idxNew = .CreateIndex("TextIndex") 
     idxNew.Fields.Append idxNew.CreateField("TextField") 
     .Indexes.Append idxNew 
     
     Debug.Print .Indexes.Count & " Indexes in " & _ 
     .Name & " TableDef" 
     
     ' Enumerate Indexes collection. 
     For Each idxLoop In .Indexes 
     
     With idxLoop 
     Debug.Print " " & .Name 
     
     ' Enumerate Fields collection of each Index 
     ' object. 
     Debug.Print " Fields" 
     For Each fldLoop In .Fields 
     Debug.Print " " & fldLoop.Name 
     Next fldLoop 
     
     ' Enumerate Properties collection of each 
     ' Index object. 
     Debug.Print " Properties" 
     For Each prpLoop In .Properties 
     Debug.Print " " & prpLoop.Name & _ 
     " = " & IIf(prpLoop = "", "[empty]", _ 
     prpLoop) 
     Next prpLoop 
     End With 
     
     Next idxLoop 
     
     End With 
     
     dbsNorthwind.TableDefs.Delete tdfNew.Name 
     dbsNorthwind.Close 
     
    End Sub