validation problem on avoid duplicate value for insert and non-exist value for update

Question

a!localVariables(
 local!insert:false,
 local!update:false,
a!formLayout(
 label: "Username",
 contents: {
 a!textField(
 label: "username",
 labelPosition: if(
 ri!readOnly,
 "ADJACENT",
 "ABOVE"
 ),
 value: ri!username.username,
 saveInto: ri!username.username,
 refreshAfter: "UNFOCUS",
 validations: {
 if(
 a!queryEntity(
 entity: cons!usernameConstant,
 query: a!query(
 fetchTotalCount: true,
 pagingInfo: a!pagingInfo(
 startIndex: 1,
 batchSize: 1
 ),
 logicalexpression: a!queryLogicalExpression(
 operator:"OR",
 filters: {
 a!queryFilter(
 field: "username",
 operator: "=",
 value:(ri!username.username),
 applyWhen:not(isnull(ri!username.username)) 
 ),
 }
 )
 )
 ).totalCount > 0,
 local!insert:true,
 local!update:true
 ),
 }
 ),
 a!textField(
 label: "gender",
 labelPosition: if(
 ri!readOnly,
 "ADJACENT",
 "ABOVE"
 ),
 value: ri!username.gender,
 saveInto: ri!username.gender,
 refreshAfter: "UNFOCUS",
 validations: {}
 ),
 a!columnsLayout(
 columns: {
 a!columnLayout(
 contents: {
 a!textField(
 label: "Password",
 labelPosition: if(
 ri!readOnly,
 "ADJACENT",
 "ABOVE"
 ),
 value: ri!username.password,
 saveInto: ri!username.password,
 characterLimit: 255,
 readOnly: ri!readOnly
 )
 }
 )
 }
 ),
 },
 
 buttons: a!buttonLayout(
 primaryButtons: {
 a!buttonWidget(
 label: "Insert",
 
 saveInto:(
 a!writeToDataStoreEntity(
 dataStoreEntity: cons!usernameConstant,
 valueToStore:(ri!username)
 ), 
 ),
 disabled:local!insert, 
 submit: true,
 style: "PRIMARY",
 ),
 a!buttonWidget(
 label: "update",
 saveInto:(
 a!writeToDataStoreEntity(
 dataStoreEntity: cons!usernameConstant,
 valueToStore:ri!username, 
 ),
 ),
 disabled:local!update,
 submit: true,
 style: "PRIMARY"
 ),
 a!buttonWidget(
 label: "delete", 
 saveInto:(
 a!deleteFromDataStoreEntities(
 dataToDelete: {
 a!entityDataIdentifiers(
 entity: cons!usernameConstant,
 identifiers:{ri!username.username},
 )
 }
 )
 ),
 submit: true,
 style: "PRIMARY"
 )
 },
 secondaryButtons: {
 a!buttonWidget(
 label: "Cancel",
 value: true,
 saveInto: ri!cancel,
 submit: true,
 style: "NORMAL",
 validate: false
 )
 },
 showWhen: or(
 isnull(
 ri!readOnly
 ),
 not(
 ri!readOnly
 )
 )
 )
 
)
)
 
 For line 17 validation part nearby, i wish the button insert will not work if it find the duplicate username already in database, and disable update button for the username can't be found, that is what i put in the validation part of if condition sentences, however, it report error with " Expression evaluation error at function a!textField", then how can I do?

Stefan Helzle · Accepted Answer

fetchTotalCount ... do you remember?

Harsha Sharma · Answer

Update queryEntity() to have fetchtotal count to true() such as 
 a!queryEntity(
 entity:cons!usernameConstant,
 fetchTotalCount:true(),
 query:a!query(
 filter:a!queryFilter(
 field:"username",operator:"=",
 value:ri!username.username
 ),
 pagingInfo:a!pagingInfo(
 startIndex: 1,
 batchSize: 50
 )))

Mike Schmitt · Answer

This is a lot of hardcoding of values. Using local variables there are usually much more graceful ways to do this, namely using a technique that I named "variable chaining", i.e. setting up a few different local variables whose values will automatically adjust based on the values of previous ones in an informative way. The advantage here is you only need to have your text field save into the "username" variable and not have a query hardcoded into its saveInto. This should be easier to troubleshoot and easier to tweak in the future. This is my own version of your above form but I believe it captures your general use case: 
 a!localVariables(

 local!name,
 
 local!usernameTaken: if(
 isnull(local!name),
 false(),
 rule!yourQueryPersonRule(
 fetchTotalCount: true(),
 pagingInfo: a!pagingInfo(1, 0),
 queryFilters: {
 a!queryFilter(
 field: "username",
 operator: "=",
 value: local!name
 )
 }
 ).totalCount > 0
 ),
 local!disableButton: or(
 local!usernameTaken
 ),

 a!formLayout(
 contents: {
 a!textField(
 label: "Username",
 value: local!name,
 saveInto: {
 local!name
 },
 required: true(),
 validations: {
 if(
 local!usernameTaken,
 "Username Exists",
 null()
 )
 }
 )
 },
 
 buttons: a!buttonLayout(
 primaryButtons: {
 a!buttonWidget(
 label: "SUBMIT",
 value: "submit",
 submit: true(),
 style: "PRIMARY",
 saveInto: {
 /* etc */
 },
 disabled: local!disableButton
 )
 },
 secondaryButtons: {
 a!buttonWidget(
 label: "Cancel",
 submit: true(),
 validate: false()
 )
 }
 )
 )
)

validation problem on avoid duplicate value for insert and non-exist value for update

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