Getting information about structures and keys

The following sections describe how to use ColdFusion functions to find information about structures and their keys.

Getting information about structures

To find out if a given value represents a structure, use the IsStruct function, as follows:

IsStruct(variable)

This function returns True if variable is a ColdFusion structure. (It also returns True if variable is a Java object that implements the java.util.Map interface.)

Structures are not indexed numerically, so to find out how many name-value pairs exist in a structure, use the StructCount function, as in the following example:

StructCount(employee)

To discover whether a specific Structure contains data, use the StructIsEmpty function, as follows:

StructIsEmpty(structure_name)

This function returns True if the structure is empty, and False if it contains data.

Finding a specific key and its value

To determine whether a specific key exists in a structure, use the StructKeyExists function, as follows:

StructKeyExists(structure_name, "key_name")

Do not put the name of the structure in quotation marks, but you do put the key name in quotation marks. For example, the following code displays the value of the MyStruct.MyKey only if it exists:

<cfif StructKeyExists(myStruct, "myKey")>
<cfoutput> #mystruct.myKey#</cfoutput><br>
</cfif>

You can use the StructKeyExists function to dynamically test for keys by using a variable to represent the key name. In this case, you do not put the variable in quotation marks. For example, the following code loops through the records of the GetEmployees query and tests the myStruct structure for a key that matches the query's LastName field. If ColdFusion finds a matching key, it displays the Last Name from the query and the corresponding entry in the structure.

<cfloop query="GetEmployees">
<cfif StructKeyExists(myStruct, LastName)>
<cfoutput>#LastName#: #mystruct[LastName]#</cfoutput><br>
</cfif>
</cfloop>

If the name of the key is known in advance, you can also use the ColdFusion IsDefined function, as follows:

IsDefined("structure_name.key")>

However, if the key is dynamic, or contains special characters, you must use the StructKeyExists function.

Note: Using StructKeyExists to test for the existence of a structure entry is more efficient than using IsDefined. ColdFusion scopes are available as structures and you can improve efficiency by using StructKeyExists to test for the existence of variables.

Getting a list of keys in a structure

To get a list of the keys in a CFML structure, you use the StructKeyList function, as follows:

<cfset temp=StructKeyList(structure_name, [delimiter] )>

You can specify any character as the delimiter; the default is a comma.

Use the StructKeyArray function to returns an array of keys in a structure, as follows:

<cfset temp=StructKeyArray(structure_name)>

Note: The StructKeyList and StructKeyArray functions do not return keys in any particular order. Use the ListSort or ArraySort functions to sort the results.

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